This is just a conversational question and I have the original BG TOTSC in mind but it likely applies to all variations. However, in TOTSC, you are starting at level 1 where this question becomes much more relevant from an RP point of view.

With auto-pause as your friend, it is possible to pull monsters to your party one at a time in a nice safe place. however, the monsters are really part of a group and in a table-top game, they would be pulled as a group.

In the example, a level 1 tank might pull a group of Gnolls one at a time and archers in the group will cut them down one at a time. However, if three of them charge at the same time, two of them might make it to the tank and there is a small possibility (0.07% if they need to roll 20 on d20 and 14 on 2d10) both of them hit and kill the tank. It jumps to about 0.72% if three make it to the tank.

I imagine there is a whole list of tactics that work in BG that would never work in a table-top game.

So the question is, do you pull groups one at a time or do you try to pull the entire group at once?

Well, yes, it's a problem with computer games lacking a real DM - things which are mechanically possible but not coherent or abusing of loopholes will get overruled by a human DM, but will happen in computer games. Up to you to decide if you want to exploit them or if you want to force yourself to "roleplay" to not use them.

Personally, I try to avoid using such tricks, but I'll exceptionally do it if I find one encounter too difficult for my current party, but don't want to just give up (or try again later with more levels/better equipment).

In BG (1 & 2) enemies attack you based on their AI script. If you attack one monster, and others can 'see' you, they will immediately join the fight. However, even if they cannot 'see' you, the monster being attacked uses a 'Shout', to call for aid in certain circumstances. If this happens, any monster within range of the shout will come to aid the one being attacked. This is a limitation of computer game AI, which as stated, lacks a real DM, and cannot work like tabletop. It's why the AD&D rules of BG are custom rules.

I remember pulling Xvarts, Hobgoblins, and Gnolls one at a time. Are you sure it works the way you describe in vanilla BG1 TOTSC?

Yes, but not every monster has a 'Shout' in their script. Some only have 'sight' scripts, which make them attack an attacker or an enemy 'in sight' only. There were also many bugs in vanilla, including scripts.

It has been too long since I have played BG2, so I have forgotten about "shout" scripts. More recently, my level 1 characters stormed the Gnoll Fortress, one Gnoll at a time.

I do remember "Entangle" being implemented differently in BG1 and BG2. In BG1, it holds your opponent still while you move your tank back and shoot him. In BG2, it holds everybody.

I have never tried a mod on BG1 or BG2 - just have not gotten around to it. It is still New Years Resolution season, so maybe I should give it a try. :)