R8300 Whether Firmware update should be done from Version 116 to 154

to be very brief, the 2.4ghz band only has channels 1-11 in north america. Because of channel overlap, they actually use more than just the 1 channel you select. In 20hz wide, you have 3 channels to use to prevent overlap and interference. Its why we usually recommend channels 1-6-11.  When people choose to go in between those channels and choose say channel 3, they're causing interference on people who choose channels 1 and 6. Not just the 1 set.  If you're broadcasting on 40hz wide channels, the channel overlap is even worse. In that cause, you'd only be able to have 2 wide and you'd choose 3 or 8 for the broadcast channels. And it causes more interference for others. 

So if you live around others, you choose the coexistance option as it limits it to 20hz wide to prevent interference with everyone else. 

You sure can choose to disable it, but its an "a-hole" move to your neighbors if you live in an area with quite a few signals. And it can even slow your network down. Reason why is if a device on the channel you're using is broadcasting, then your device has to wait its turn to broadcast. And if you're overlapping on more than the one set of channels, the chances of another device broadcasting increases. 

There's a ton more details than this. 

If you want to read more or see a chart about what I'm describing, read a little on 2.4ghz channels. 

https://en.wikipedia.org/wiki/2.4_GHz_radio_use

Basically it comes down to, if you live close to others, leave it enabled. IF you live in the country where there isn't much interference or 2.4ghz, then disable it.