Timing.
I'm practiciing the bluegrass songs I've learned with a metronome now.
I've got it set way slow, slow enough that I can actually do all the rolls
and hit all the notes. And it is helping with timing. I only downloaded
the metronome into my phone a week or so ago, and already I can
play the songs noticeably (by me
anyhow) better and faster when not
using the metronome.
-Mike