I don't run modules. Among other reasons, because they are built with the "balanced party" in mind and often have parts that are virtually impossible to surmount without specific skill sets present.In character, it only makes sense to have a well-rounded skill set in the party. A lockpicker-trapfinder-scout is an obvious skillset any party is going to need - or will soon enough realize it needs after any time in the field; and so if it looks like we're about to set off without such a person then dammit, I'm going to go and recruit one.
Same if on preparing to leave it becomes obvious that a party I'm in doesn't have a front line, I'm going to go and recruit a warrior or two to join us; be it as henches or as full party members...even more so if we've already tried the no-fighter approach before and got our butts kicked.
This allows players to play what they want to play, e.g. if everyone wants to play mages or rogues or other backline types they can, and not be or feel forced to play something just because we need it; while still putting a more complete party into the field.
Also, what do you do when running a module that for whatever reason gives the party an NPC adventurer, be it as a rescued prisoner, a plot device, a spy, or whatever? I-3 Pharaoh's Tomb expects the party to find and take in (two? three? I forget how many) adventuring NPCs during the course of the adventure as they explore their way through the pyramid. WGA-4 Forgotten Temple of Tharizdun expects the party to rescue and take in an NPC adventurer who very much has his own agenda. This sort of thing is common.
In fact, some of my favorite campaigns were ones where the party was made up of a single archetype.
I also don't do the DnD thing which I have found makes it much easier to have PCs that can handle challenges outside their specialty as the rules allow for PCs to have secondary and tertiary skill sets.
In most of my campaigns the magic user can also swing a sword, warriors are able to sneak, and the scholarly priest might even be able to pick a pocket.