If you're talking about a DSL modem/router, 99% of the wireless ones also have 4 ethernet ports. So, you can enable the wifi for a PC in another room that's doing things not as dependent on the stability of a connection, like web browsing. But you will still have the option of a wired ethernet connection for when you need to have reliable and responsive broadband, as in multiplayer.
Personally, i have extended my line to my PC desk so i don't have to mess with wireless at all. It's not that you won't get good speeds and reliability from wifi, it's just that there are less things to interfere with a wired connection. Now if the construction work near my home finishes and they cover up the ditches they have dug in the roads i will get my reliable broadband back. The power company and another ISP are both working there and it's playing havoc with lines in general, autumn rains don't help either as the ground gets soaked and they get interference from moisture.
I'm constantly capped at no more than 10Mbits on a 24Mbit connection and have disconnects and time outs all the time. Just goes to show that no matter how careful you are about setting these things up there's always bound to be something that's beyond your control, so i prefer "old fashioned" but tried and tested methods most of the time to minimize the amount of things that can go wrong
