Seems like Chastity can have different uses and definitions for everybody. That, along with so many different reasons that might get one to desire or actually require chastity,It really is not a one size fits all kind of thing. I think it really boils down to what or how can it positively impact and ignite 2 people in a relationship.
Self locking is another aspect that may or may not include a "partner" but can certainly help prepare somebody for the day that they do get into a relationship with another person, whether online or in real life.
As far as "cheating" goes .... that also in my view depends on each individual and or relationship to define. I have a device that is easily cleaned without taking it off, I also have several that after a day or two, it gets waay too funky and needs to be taken off for hygienic reasons. There is a realistic aspect of real life and long term chastity. At least that is what I have learned over the last few decades of being into this kind of stuff.
Here is an example of my most recent experience or lock up: Was locked up on Aug 2nd when the wifey started her period. She has kept me locked since. However, she has let me out a few times each week for teasing and PIV ... of course without any orgasm. During the 3-4 PIV sessions, I was leaking like a freshly poured draft beer ... it was just going everywhere, but definitely very short of an Orgasm. Perhaps it was similar to a milking? I dunno . again all up to each to own and define I guess. Point is, for "us" it certainly was not cheating as the wifey has the keys and controls the lockdown and or outcome or lack of. I have given her the control and I will accept whatever she desires.
Lots to chew on with the original question and it sure can go a million directions. ymmv.