After warming up(I consider myself warmed up when I can alternate pick chromatic runs at 120bpm cleanly with some ease)Its way too easy to just play my favorite riffs and licks instead of actually 'learning' something new or working towards a goal.

There is a HUGE difference between practice and playing.I can PLAY for many hours,but can only concentrate on specific efforts for an hour or two.Its taxing on the body and mind to try to 'hardwire' anything new to memory/muscle memory.