

Then you really should list all of the secondary functions you plan to add to it, make sure they understand what those are, and agree to each of them: full disclosure.
If you do something on it that could get them in trouble, it’s their ass on the line, not yours.
Counterpoint: Good?
The fediverse has no global identity system. Just like how temporary email addresses protect YOU from spam, disallowing them protects volunteer-run services like Mastodon, Piefed, Lemmy et al from spam (and trolls, etc).
I do not approve any registration applications from throwaway email providers. Also, volunteer-run services are much less likely to use your email address for nefarious purposes. Data breaches are another thing, but TBH, most of the spam I get is from spammers just spraying out to anything that’s formatted like an email address. Not sure about Mastodon, but Lemmy and Piefed do not reveal your email address to anyone (admin can only see it during singup and in the database). At least in Lemmy, the passwords are hashed, but the standard advice to use a unique password per service applies so that in the event of a data breach, the email+password combo will only compromise that single service.
I guess the moral of the story is to save the tinfoil hats for BigTech™ and show the Fediverse people, who are trying to do better, that you’re here with good intentions. As an admin, I’ve seen more spam, trolls, and n’eer-do-wells signup with throwaway emails than people who are here because they want to be here, and to a severe enough degree that I will no longer accept registrations using such services.