As is with the normal game mechanics, most peasants and workers do not move quickly. The "Speed Glitch" is (usually) a deliberate exploitation of this glitch in an attempt to gain an advantage, ergo I would consider it a "cheat". For all intents and purposes, however, it's nothing huge to worry about.
To differentiate from a glitch and a simple exploit, I'll site the case of the "anti-assassin wall"
It is normal in the game for units to not be able to stand on 'high' parts of the crenelation. It is also normal for the game (for some odd reason) to make all points of crenelation 'high' if they are placed as adjacent rows. Therefore, it is normal for the game to make these two layers of unoccupiable walls. Since the sins have no place to stand once they climb the walls, it's only natural that they can't climb the walls. Else, if they could climb the walls, they'd simply disappear once they reach the top.