It entirely depends on what they were carrying - If it was a Plasma Pistol, you will get PP clips. It's clearly going to make a difference on what they were carrying.
I recommend taking Laser Pistols/Rifles to every battle. Laser Pistols are always handy for when you want to shoot a wall or whatever without wasting ammo and weigh almost nothing.
Laser Rifles are a different issue altogether. They weigh about the same as a Rifle and do a bit more damage, but with less Accuracy (I think). They also need no ammo and are very useful in shootouts with pretty much any alien, they can harm nearly all of them.
Heavy Plasmas will flatten a Muton in one shot, no doubt, but even if you know that you won't run out of ammo, the thought is always there. If you want to take any more clips, that also adds to the weight and inventory space used. For this reason amongst others (you don't need any Alien Alloys to make them either) I prefer a Laser Rifle.
On the other hand, 2 Marksmen/women with Heavy Plasmas can come in pretty handy, as Heavy Plasmas weigh the same as a Human Rifle so they are not hard to carry. On the other hand, the space for clips could be taken up with HE, one of the best items in the game (XcomUtil makes them do 200 damage
).