I guess this is advice specifically for if you're a therapist, or a not-really-a-therapist-but-acting-as-one such as a manager trying to support an upset employee. The distinguishing part of these conversations is they're not symmetrical - the focus is supposed to be on one person much more than the other.

(Maybe "if they're crying, don't relate" would be a more focused heuristic.)

In an everyday "you've met someone and want to get to know them better" situation, relating sounds like a good thing all round: they share something about themselves, you share back with something related about yourself.