It's a little like "unlimited holidays". If you turn up on day 1 and then say "Right, I'm off on my unlimited holidays! See you never!" and disappeared, they would stop paying you. There is an implicit fair use clause in all unlimited offers - I know a guy who pushed back on "unlimited holidays" because he didn't want to get penalised in performance reviews and it turns out that in his UK-based org it was 29 days a year, or one day more than the legal statutory minimum.

Firms like penpot are basically saying "look, if you pay us this much, we're not going to put hard quotas on you, just get on with it", but if you then try storing backups of annas archive on it, they are probably going to suggest that you are not operating within the spirit of the agreement, even if you're within the letter of it: fair use will apply.

Some people like to know where they stand. They want hard quotas. So fine, ask them for hard quotas. Ask for the fair use clause and understand it.

Most of us know what it means (it's a soft quota with fair use limitations), and are happy with not abusing the tier and having a bit more freedom, though.