We hit a case in T7392 where a user sent a diff, but then declined to sign the CLA. In the strictest legal sense this sort of taints the diff, since if I merge some similar change after looking at the diff, it's arguable that my change is derivative rather than an original work. This gets somewhat perilous for trivial bugs with a small number of reasonable fixes.
It's hard to roadblock users on the diff creation pathway, since diffs don't trigger Legalpad and it's hard to pause revision creation and resume it later (e.g., if "arc" exits, the user would have to go through a bunch of stuff again after signing the CLA).
However, we could hide the text of the diff until CLAs are signed, effectively preventing anyone from being tainted by it.
This isn't really a huge deal and I doubt a litigant would prevail by claiming we stole their 4-line trivial change, but this seems like a reasonable way to approach the issue more cleanly and enforce propriety in CLA handling.