General

@Burning: Yeah, I just checked and the article I was reading about dual band compatibility was from a few years ago.

If smartphones and tablets are the only devices using the WiFi though, it's unlikely any benefit will be had from using a dual band router unless there's an awful lot of 2.4ghx interference in the area.

[quote=BobR]...smartphones and tablets, and those DO need WiFi. BUT- those devices won't work on the 5.0ghz band, so that capability would be wasted...[/quote]

wat

All current generation flagship smartphones from the major manufacturers are dual-band wi-fi compatible. A few before those were also dual-band compatible. Ditto for tablets.

@iYanMe And to simplify it even further-

If your computers are all connected by cables, you DON'T need a wireless router for them at all. Single band OR dual band.
However, you mentioned smartphones and tablets, and those DO need WiFi. BUT- those devices won't work on the 5.0ghz band, so that capability would be wasted.

In your current setup, it sounds like a dual-band WiFi router is overkill.

Uh yea, so I'm going to make this more simple than what has already been presented. Not surprising since you restated the question and BobR buried the answer to that question deep into the post within two sentences.

[quote=iYanMe]Which band should I connect smartphones, tablets, and laptops too?[/quote]

Doesn't matter. Houses don't usually have serious problems with radio interference because of spacing. Giving one device its own band separate from the others is certainly something you could do.

[quote=iYanMe]If I connect them to a specific band, will it affect the speed our desktop computers when streaming from amazon?[/quote]

Only if the wireless devices are using internet bandwidth at the same time the desktop is streaming. Otherwise, no, as most modern routers have a DHCP table capable of assigning more than enough IPs on a home network and enough processing power to handle the connection load.

[quote=iYanMe]If it has absolutely no useful benefits for us then I think I will return it and purchase a non dual-band one.[/quote]

So this is where I'm going to summarize the relevant information regarding dual-band wi-fi technology. I can't make this decision for you because I don't know how your gear, house, and neighborhood are laid out or set up.

Dual-band wireless is intended primarily to solve the problem of signal interference with traditional 2.4 GHz wi-fi networks. This is most commonly observed when many 2.4 GHz wi-fi routers are in close proximity to one another, such as in an apartment, and the wi-fi signals on the same channel interfere with one another causing data loss. 5 GHz does have tend to have higher transfer speeds than 2.4 GHz, but that's only important to heavy home network users such as those who have a home data server or do remote streaming. Otherwise, internet speeds are determined, and therefore bottlenecked by the ISP connection outside of the house.

2.4 GHz
Pros:
*Much longer range than 5.0 GHz - distances up to 500 feet are possible
*Virtually all wi-fi devices are compatible with 2.4 GHz technology
*Generally less expensive to buy a single-band router
Cons:
*The proliferation of 2.4 GHz routers in crowded urban environments creates the problem of signal interference

5.0 GHz
Pros:
*Fewer 5.0 GHz routers as well as the signal's smaller range means less signal interference when connected with this frequency
*Sometimes higher data transfer speeds are possible on the 5.0 GHz band (ex. a router with 750 Mbps is actually 300 Mbps on the 2.4 band and 450 Mbps on the 5 band)
*Dual-band routers allow for at least two separate devices to be connected at different frequencies. Two devices could each have their own band entirely to itself.
Cons:
*Much shorter range - 50 feet I would say to be the farthest, though troublesome routers can have a range of just 10 feet; walls will reduce effective range
*Not all wi-fi devices are compatible. This works both ways - a 5.0 GHz smartphone will use 2.4 GHz when connecting to a 2.4 GHz router, a 2.4 GHz smartphone will not be able to access the 5.0 GHz band from a dual-band router
*Generally more expensive to buy a dual-band router

Well then, I think I just wasted an extra 30$ for a router that I have almost no use for since all my the computer at my house are connected through cables.

Which band should I connect smartphones, tablets, and laptops too? If I connect them to a specific band, will it affect the speed our desktop computers when streaming from amazon? If it has absolutely no useful benefits for us then I think I will return it and purchase a non dual-band one.

Most desktop computers don't come with a wireless adapter built-in.
If you need wireless because of the distance from the router, you can buy either an adapter board you install inside the computer or a USB adapter that just plugs into a USB socket on the computer.

Or you can just run an ethernet cable from the computer's ethernet socket to the router's LAN socket.
A direct cable is best, better reliability of the connection and highest speed. Wireless on the other hand can be easier over longer distances.

Examples of wifi adapters: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100010074&IsNodeId=1&Description=wifi%20adapter&name=Wireless%20Adapters&Order=BESTMATCH&isdeptsrh=1

The 5.0ghz specification refers to the radio frequency used to connect between the computer and the router.
The higher radio frequency may allow a somewhat more reliable connection between devices by avoiding interference from other devices.
This doesn't affect the transmission (download) speed you can get, the main factor there is the kind of broadband service you're buying from your ISP.

Also, you'd have to be sure to choose a wireless adapter that can match the specifications of your router to be sure of taking the best advantage of the router's capabilities.