There's really few games in the genre, and few genres, that could exist without pathfinding, and without good pathfinding/AI, it becomes a crippling wound to both the development and gameplay of the title.
Here's the thing about pathfinding and AI in general.
RT comparatively and completely sucks for excellent pathfinding, AI, etc. Correction, it sucks when you have many actors on the screen at once, and thus either the capabilities of each calculation for individuals must be cut down or the actors must be limited in number on a constant basis (see the Radiant AI issues). FP is also often used as the control scheme doesn't require that the player characters to have pathfinding routines as in click'n'move controls.
In free roam, out of combat, NPC pathfinding can be handled by a movement script, to follow along predetermined paths. They usually tie in well with schedule engines. The only real non-static movement would be by the player characters and anything special/initiated by the players. The actors on the schedule routines can be easily switched over to a full AI when combat is initiated (even if it's just to flee, depending upon the actor flags set), without any noticeable stutter in gameplay performance. A lot of RT engine stutter is from switching an NPC or several between routines. Not all engines can smoothly switch over heuristics from one routine to another, and so the routine starting up eats into CPU cycles to gather the bit of data it requires to function. When you talk to a roaming character in a movement script or otherwise act with them, you will often see a skip in action unless your computer's specs can outweigh the draw of resources by the starting routine.
Tag-along pathfinding, as typically used in escort quests, is a relative pain to do well because it constantly changes and needs to find a movement resolution for the follower on a constant basis. Most times it's a simple line, and so the escort is caught behind a simple object. Other times, devs cheap out and make the escort go along a scripted path.
Where it becomes a big issue is during combat, which is also where errors cause the most problems. I've had the Inbred Engine cranked to max and still had characters who couldn't find their way to the other side of the map; they instead just dryhumped the side of a simple, squareish building. Without handholding a mage, I've had them run up to a pack of enemies and point blank a fireball spell when I had them target the critter. That leads me to believe the range finding was borked somewhere, or got lost in the mess of other routines. Dropped heuristics from database overflow is a sadly common thing for most RT games using a lot of actors at the same time, and it's not a good thing.
In TB, writing AI/pathfinding is INSANELY easy and offers far more capability. As the defining characteristic of TB is that one character moves/acts at a time, a lot more CPU power can be given to calculation and heuristic depth for that one instead of 10 or so at the same time. Yes, that means effectively you could use ten times the power - OR MORE - on one character in TB than you could in RT. RT is hindered by another sad thing that tag-along pathfinding suffers from - as each actor moves, EVERYONE ELSE has to constantly re-adjust their heuristics to follow and react accordingly.
TB adds more capability for challenge, as they can write real AI routines instead of using "shortcuts" or stacking stats against the player (leading to comments like "This fucking AI is CHEATING!"), and this is likely why most games of late tend to have really easy enemies or pull shit tricks like many racing games.
Oh, wait, TB gets even BETTER! Since it calculates each in turn, and in greater depth, it can keep a rolling set of heuristics for subsequent actors/turns. It also allows for a much more complex integration of teams/allies. I'll use an example from X-Com. When one alien would spot one of your troops, through telepathy the others would also know. This can be expanded into mechanics like a policeman actually using time units/turns calling for back-up and to further report on a suspect, as the remote actors take reports from those in the immediate area of combat. This is done in several rudimentary forms in RT games, but it generally doesn't go much deeper than the police pursuits in Grand Theft Auto, where police magically appear out of thin air in whichever direction you are heading.
