It stops the automation part. One LLM spammer can be dealt with.
One can focus on generating 10 other accounts before it's flagged. Now you have 10 others to deal with.
But that does not work on lobsters (or anywhere else with gated registration), because you cannot just create 10 accounts. You can create 1 account after 1 invite. If you abuse, you loose the invite (and maybe the person inviting you the right to invite others).
I think, if i have understood the answers correctly that it's stopping a quick proliferation - but not a long slow infiltration?
The spam bots I regularly deal with on reddit are using accounts that are several years old. I'm not sure if they are hacked, purchased, or something else.