Say I am in the goblin temple killing the bosses, I have 2 in the room with the dead illithid, and 2 left over were I killed Minthara (or where I freed the guy being tortured which would be even longer if they automatically engaged from there), I do not want to spend at least 4 turns to run them all the way over to the fight when I can simply engage with the 2 in there, and then have the other 2 in the next rotation. The way it works now is just fine.
Not to having to wait for units not engaged in combat to process their turns. Turn-Based combat bubble is a good and practical design - and allowing a coop player to run to the encounter is better then reloading even if it breaks all laws of physics. The only issue I see is stealth units not getting included in the bubble. I found it odd in D:OS2 but In BG3 if felt worse and more exploitative. I don’t think that using stealth should feel like breaking the system.