"Cishet" is like any other term. It can a good shortcut be best used to describe those not transexual and/or homosexual (or otherwise not entirely that side of binary) because "not transexual or homosexual or otherwise personally affected by LGBTQI+++ issues, but sympathetic to the problems" is often long-winded, or it can be thrown at (deserving or undeserving) anyone perceived as not an "us" by the rather more militant tendencies in the non-cis/non-het community who are maybe a bit less than amiable with their perceived 'normie' persecutors.
(Ditto 'normie', 'neurotypical', 'white', 'woke', 'liberal' and (inversely, in various ways) 'queer' and the N-word. Maybe not always necessarily a badge of honour, for the membersip, but not automatically a condemnation unless the caster of the term intends it to be an aspertion upon the target. The latter two also tend to be terms only to be used to describe yourself (or if explicitly invited to by those who can do by dint of their own membership, in very careful circumstances) otherwise you might easily get thought to be using it detractingly, after being successfully reclaimed for the "us" of the respective communities from the one or other degree of historic "anti-Us" usage . Especially the N-word, but I'd probably not casually use the Q one to(wards) someone's face either. Except entirely in the more innocent Enid Blyton context.
But I'm happy to be thought of as cishet, in an "allied" way. As much as there's any accuracy to such an absolutist term. Having it thrown at me in a slanging match from a non-cishet individual who seems to think I cannot be an ally would be saddening, but mostly because of their own prejudices, not because it is prejudicious in and of itself.
Of course, in a text-only community like this, the cues to work out how it is meant (and taken) are limited to the explicit (or the aftermath) and leaves open the possibility of my being called something and I take it as a complement.
(Or I choose to. I've been called a "jannie" by some 4chan-inspired wannabe, in another locale recently, and it just amuses me to think/say, that yes, I am keeping the place clean and helping to clear up your deliberate mess.)