We ban jellies by the dozen almost every day for spamming. As for established, non-spamming jellies, it hardly ever happens. You’d have to demonstrate a flagrant, willful and repeated disregard for the rules to actually get banned. There would be warnings and probably a suspension before that happened. An exception to this might be a “spoof” account set up by an established member in addition to their main account; if for some reason this spoof account violates the rules, it could be summarily banned without actually banning the user.
Which brings up another important point: suspensions are not the same as banning. They may look the same from the outside (user-deleted accounts, suspended accounts, and banned accounts all display the same way). Some suspended members have even claimed to have been banned. But a suspension is revokable after a specified time period.