Astraeus

I feel that trash mobs play an important role in a number of ways, one of the most important of which is in demonstrating character power progression. At the start of the game, one or two low level monsters should pose a challenge to your character, yet a few levels in, after significant character and story development, the PC will be facing tougher, higher level foes yet should be given plenty of opportunities to massacre the same low level mooks who once posed such a threat and let the PC's progression in the world be demonstrably real. If trash mobs are removed, then progression becomes an illusion, a treadmill, where all that changes are the names and graphics of the PCs opponents and the relative challenge of PCs vs foe remains constant. The fact is, I want my PC to be a badarse who can slaughter swathes of lesser opponents even as he remains challenged by higher level enemies. It all depends on how intelligently encounters are designed though (and I feel Obsidian is brilliant at encounter design, eprsonally). If all you're doing is engaging in intermittent meaningless slaughters or randomly placed trash mobs, that's simply a chore, and lazy design to try and add something into an otherwise uninteresting or empty, low gameplay density, most likely wilderness area. I know some people loved it, but that's one of the reasons I disliked much of BG1, where I found myself simply clearing fog of war out of my completionist instincts and barely noticing the trash mobs sprinkled through them, as I hoped to find something that was actually significant or interesting... I also feel that trash mobs can contribute positively to encounter design that includes higher level opponents. They can enhance the apparent scale of a battle in a way that multiplying non-trash mobs can't (you'd simply make the battle impossible for the PC if you fill the screen with tough enemies), and add a tactical element in that in numbers, even trash mobs should pose some minor threat, if not to the PCs health then at least tactically in terms of blocking the path to ranged enemies and the like, and the PC needs to decide whether to spend any effort to clear them from the battlefield, or to ignore them and focus on the more significant threats.