For those that don't know P-T-E is the PC default buttons to go to Party->Leave Instance->Confirm
It's something that can be done incredibly quickly and is a really nice feature for quickly leaving the instance to reset it when going for a no death achievement.
There have been some questionable applications of this that has led to a lot of small arguments, largely amongst the endgame PvE community.
Some examples ranging from relatively harmless to potentially considered an exploit:
You died in a place you are not revivable so you leave the instance to rejoin the fight
You are accidentally wearing the wrong gear set/ wrong skills once combat starts so you PTE, fix your setup, and teleport back into the trial.
You know you're about to die and rather than throwing a no death you PTE.
You leave the instance to negate/cancel an intended group mechanic to make a fight easier or faster.
Over the years while ZOS has never given an official position, they have attempted to make a lot of changes to remove this behavior.
Most of which were very disliked by the community, primarily due to unintended bugs:
They removed the ability to use PTE while in combat
Problem: Very frustrating if you end up stuck in combat, or just if trying to reset an instance after a death you have to make sure everyone dies before leaving
This was eventually removed I assume due to community frustration.
After re-enabling PTE in combat, they made it so leaving an instance in combat counted as a death.
Problem: If a player crashed in a relatively harmless area, between bosses, but the group was in combat. They lose vitality and their no death achievement.
An even worse problem that was repeatable in a few instances, if players strayed too far from the group leader or went through a door before others, it would occasionally count that as them leaving the instance and the group would lose vitality.
This feature was understandably removed due to causing so many groups to lose no deaths strictly due to bugs/ connection issues.
That brings us to now, where there is no feature trying to stop PTE-ing.
I've started to see discussions in raiding guilds about whether or not it's okay to do, people strategizing whether or not they could leave an instance during downtime in fight to swap their gear and if that was considered exploiting or fair game.
Since there's no ruling or opinion from ZOS we have nothing to go on beyond our own beliefs and ethics about it.
As far as we know no one has gotten in trouble for it, but its not something I or many would like to do without knowing it's considered fair game.
I'm not looking to get anyone in trouble or punish players that did this unknowing if it was okay.
I would like confirmation if this is something that's fine to do or not, so I can warn or dissuade others from doing this in the future if it's the latter.