Another question!!! I'll have to charge you!
Depends, it can have a detrimental impact on battery life. I wouldn't generally bother with it unless you have a particularly weak wifi signal and it drops out constantly.
I only use it at work where the wireless router is relatively far away. At home, there's no need as I'm never really more than 30ft away from my router.
There's no harm in turning it on for a bit, see what impact it has, but you should be fine to leave it off.