It lets you understand the code base at reduced granularity when you want. Or zoom in beyond the written lines to explain _why_ some code is the way it is.
Claude in its default configuration has untapped potential for explaining and documenting code because it defaults to writing no comments. I added this to my global CLAUDE.md and so far so good:
# Comments
Keep existing comments unless they're wrong
or stale. Err slightly toward adding short
explanatory comments for non-obvious code.