You'll need the reserves for when things don't go as planned (which is often!)
Tell me about it!! :D
My challenge has been knowing what that capacity is (and for that matter, being really clear on what I'm committed to.) That's what I'm working on this year.
THis is something that I used to know in myself, but no longer have a sense for where that edge is. My memory remembers the old me, but doesn't know the new. Good luck this coming year of getting on track :)