My rental is really hard to comp. It's a 3 bed, 3 full bath duplex-style townhouse. Nearly everything else in the area is either a large single family, or an apartment (or apartment-style--meaning many units and multi-story). So comping it is rough. But the PM and I chat each year and figure out what we think is FMV. If there is an existing, solid tenant, we aim for the bottom of that range or just below. So probably not quite at FMV, but not hugely under it, either. When listing for a new tenant, we go further up in what we think is a fair range, but the understanding is always that if it isn't rented in 10-14 days max, then we drop the price a bit. Haven't had to do that yet though.
Clearly, I want to get as much money as I reasonably can. But I also want to keep good tenants and avoid the stress and expense of a turnover (even a short vacancy has costs). And I want a new person to feel like it is a pretty good deal, so that we get lots of interest and so that we can attract and keep someone longer term.
One other thing to consider is that if you don't at least come close to keeping up with FMV, it gets harder and harder to get back there, because doing so would mean a massive increase. If $100/mo seems like a lot and you do $50 instead, and you do that for three years. Then you need to raise it $250 to get back up to FMV. If it is awkward to do $100, it will be painful to do $250. And the lower you sink below FMV, the less likely you are to have the current tenant move out, so waiting until you have a new tenant and clean slate doesn't necessarily work so well, either.
When I tell my PM what I want the new rent to be, I usually also tell her that if the existing tenant balks, I'm willing to accept $x less to keep them. So I'm also wiling to work with them, and show I'm working with them. But that has never happened. Maybe that means I have the formula just right. Or maybe it means I'm underpriced. lol
So yes, I think it makes sense to be somewhat conservative in increases, both due to expenses of turnover, and to goodwill, which it never hurts to have with the person who has day-to-day control over a huge asset. But not to just give it away, either.