I think undervoltage is more a protection for the power source side (grid/generators).
For consumer side, essential protections are current based. Undervoltage is mainly used for load schedding issues.
Useful to prevent motors running on a single phase. Utility here specifies that the voltage shall be between 540 - 636 V.
So, we set our UV's at 90% with a time delay of 10 sec. to avoid nuisance tripping.
We use 27 relays for several applications. They are a permissive relay for certain breaker reclose conditions (Hot Bus / Dead Line). They are also a tripping relay in some instances. This is usually applied on a transmission bus that is connected to non-conventional generation. In these cases, generation is on the low side of a substation transformer, so their is no zero sequence path for ground faults. The only way to detect a transmission ground fault from the perspective of generation is to sense low/no voltage on an individual phase. USUALLY though, this would be accompanied by a zero-sequence over-voltage relay.
But I digress. This is probably not the application you are concerned with.
There are no universal answers, every application is different. If it makes sense to trip on undervoltage then trip on undervoltage but if it doesn't make sense to do so then don't. Sometimes "what makes sense" will be clearly spelled out, an interconnection agreement for instance, and sometimes it's up to the protection engineer to figure it out. Where you are plays into it too, what is commonly done in one part of the world makes no sense elsewhere.