Hi there! I think it depends on what you’re aiming for, as each practice strategy can have a different purpose. For me at least, there is a difference between chunking for practicing, and chunking for performance. I’ll go into chunking for practicing here:
Suppose I have a 4-beat-all-sixteenth note lick:
1 e & a 2 e & a 3 e & a 4 e & a
For performance, say I want to slightly stress the beats (1, 2, 3, 4), because that fits the music. Each beat will likely become a chunk, because that’s what I want to bring out, and it keeps things clear in my head.
For practicing
I believe this is slightly different from the concept of “chunking” as covered by Troy and some others, but it’s still a great concept and addresses your question.
During initial practice, I feel it’s best to break a lick into chunks, and practice them all separately, both slowly and and speed. So, if your chunk is just each group of four notes, you’d practice “1 . . .” until it’s even, then “2 . . .”, etc etc. Alternate fast and slow practice for each individual chunk: slow to understand what you’re doing, and fast to ensure that what you’re doing actually works.
When you’re practicing, adjust your chunks to keep your brain involved and happy. For example, I hate practicing just “1 e & a” sixteenths, b/c my brain really wants the extra beat … so I’ll play, eg “1 e & a 2”, adding the extra note.
Chunking also lets you focus on problems. In the above lick, everything might be super easy, except for the “& a” of “3 e & a”. So you can spend more time on just that chunk. Practice the hard stuff.
If you practice each chunk separately like this, you will likely run into problems when you start joining the chunks together, for a few reasons: you may accumulate tension during playing, you may have slightly different hand positions, etc. For this reason, it’s good to consider at least a few notes before and after each chunk, and sometimes play them, to get the “physical context” of each chunk. e.g., instead of just “1 e & a 2”, it might be good to play “1 e & a 2 e &”, to ensure that you’re practicing chunk 2 in the same way that you’re really going to play it.
When the individual chunks are working well (fast, clear, and easy), join them together, one by one, and practice the slightly longer chunks if needed. E.g, you might start joining 1 and 2, and separately practice 3 and 4:
1 e & a 2 e & a 3
3 e & a 4 e & a
This may introduce some new problems, so again do slow and fast practice.
Then join everything together – new problems, same solutions.
That won’t work, because it’s not focused enough. It’s good to do, but only once you’ve achieved speed. Similarly, practicing a whole lick quickly might not work, because you could be glossing over problems, and not addressing them. Chunking for practice often lets you find and solve individual problems.
Hope this helps, jz