Having tried everything from super large area (full area on CTH-470) to super small (about 1cm width) this is my thoughts:
Large area:
Pros:
-Very precise for jumps that are not extremely fast
-Very precise following streams + fast sliders
-More margin of allowable error when hitting notes
-Easier to build up muscle memory (slightly)
Cons:
-Making repeated large movements can be tiring for fast maps
-Fast back and forth large movements can be inaccurate (on DT, fast far jumps etc)
-Grip on pen more prone to randomly slipping as you're doing fast large movements
-Hand more prone to slipping on tablet surface (again, larger movements)
-Too large of an area can result in spots (top left and bottom right corner assuming you're right-handed) that are more difficult to reach, which can result in randomly missing stuff that appears in those corners.
-May have to grip the pen higher to reach the whole area, which is (slightly) less precise.
Small area:
Pros:
-Very fast to react to notes
-Very easy to reach everywhere on the map, so no spots that are hard to reach
-Small movements, so they can be done back and forth with higher precision for fast jumps
-Can grip the pen lower
Cons:
-More prone to shitmisses because less margin of allowable error
-More prone to random slider breaks, same reason
-Harder to build up muscle memory
Imo the best thing is to go for a medium area and not go to either extreme.