In using the beta, I haven't noticed any actual performance/battery difference between the two. Honestly, when I first installed it the first thing I noticed was the lack of sound when changing the volume.
It's still there, but now you hold shift+vol up/down to hear the feedback. This is in contrast to earlier OS X versions, where holding down shift will mute the audio feedback.
Heh, me too - you can turn it back on in System Preferences though. It's a new sound effect.
Do you know exactly where? I couldn't find it.
I don’t have Yosemite, but in Mavericks, you can change it in System Preferences > Sound > Sound Effects, by checking the checkbox “Play feedback when volume is changed”.