I've read on the wiki that it's good to have 3 tile wide passages so dwarfs don't have to "crawl over each other", but how much of a problem is this really? At the entrance to a fort it seems most ideal to use a 1 tile wide passage so you can force enemies into a series of traps, war dogs, and whatnot.
As far as this goes, you can get the best of both worlds by having your entrance go through a 3+ width tunnel, but also having a means to close down the tunnel's width to 1 width. For instance, if you've got a 3-wide tunnel, have there be lines of drawbridges along both walls, raising towards the walls, so that the sides become inaccessible when a lever is pulled. Alternatively, have them be retracting bridges over deep channels, and you've got the makings of a dodging trap.
Generally, it is believed that wider pathways help both fort efficiency and FPS to an extent. Once you've got hugely wide hallways, dwarves will take the shortest route, which will tend to put all paths at corners, so there will be collisions at corners regardless of whether you've got 3-wide, 5-wide, or 99-wide hallways.
In addition, the wider the hallways you have, the more possible paths that the game has to calculate, so widening halls can hurt FPS, though since the pathfinding algorithm appears to go around creatures whenever possible, having wider than 1-width halls will allow it to go directly around a blocking creature instead of halfway around the fort to find an alternate path, helping FPS.
In short, hallways that are 2-5 tiles wide, depending on expected traffic, are more-or-less ideal for all concerns except defense. Much more than that and you stop having hallways and start having long rooms, and single-tile halls cause repathing issues and so are less efficient.