There are many good reasons to use miniatures and models for your role playing games. Apart from the fact that they are visually pleasing they also help DMs and players alike with area of effect and terrain features. What better way to simulate a city battle than by laying out buildings provided by Miniature Building Authority or to delve deep into a cavern complex or dungeon using the beautiful models from Dwarven Forge.
Plastics versus Metals
Of course there are people in both camps about plastics versus metal miniatures. Me, I prefer the plastics for monsters etc and the metals for players characters, important npcs, and villains. It has been said at my table more than once "Oh he is a painted metal figure, he has feats." The players are of course right in that assumption.
The good thing about plastics is you can just toss them in a box. I keep mine separated by type and by usefulness. For instance, all of my humans are in one of those plastic trays with the drawers used for crafts. I have them separated by rogues, city guard, wizards and clerics, bag guys (Zhents, Cult of the Dragon, other cultists etc) and by rangers. In the top drawer is where I keep all of my thrikreen, Ghale and other strangeness. I then have a box full of fishing trays with the undead, elves, dwarves, animals, drow, lizardmen, etc. They are in separate areas of each box. For my larger figures I have them in the dollar plastic shoe box sized boxes you can pickup at the local mart store. I have them labeled by type as well, Dragon, Giant, Demon etc. My metals are arranged very similarly in chessex type boxes in order to get to them quickly. What I like about this approach is that I can actually use random tables and pull anything I need right away. It is very useful.
Buildings vs Mapsheets
For me it is not a question of either or but of using BOTH. That's right I like to use both actual miniature terrain AND mapsheets in my games. Right now, for instance, for Friday night I have the MBA buildings I recently picked up from Kirk on the table to use for the town that they had crashed in. I will be using the buildings as representations but what wonderfully beautiful representations they are! Underneath the buildings I have several Piazo and Scrying Eye games maps to use for other things that are in the town.
Pros and Cons
While yes it is true that some players like to metagame with the scale of using the mapsheets and buildings, it can be very rewarding to have players use these types of tactics in the game. As a DM you will just have to decide if you want to encourage them to use battle field tactics or you do not. Undoubtedly it can be challenging for a DM to use maps when they are used to not using any maps or terrain at all as most players quickly realize they can count squares to figure out the distances where there enemies are and the exact placement of spells. Is it realistic to allow them to take the time to figure out exactly where to place that spell? No. You could tell them they have one chance and have only a minute to decide where to place it. A minute is my standard time per player during a combat phase anyway. This would give them the ability to be tactical but also give them the feeling that they are indeed in the middle of combat.
In conclusion I say use them. They are a great game aid and come in handy at a tabletop rpg!