I've previously described one of these (types of) motions and have explained how they are practiced against the common manors utilized in an assault (like those listed above).
Very often, it seems that systems will attempt to have students practice defenses for manors of assault that are more appropriate in an action movie, than in a typical assault.
The situations listed above, are far more common than what are more often seen practiced in the average school/dojo. Many schools attempt to have students practice against aggressor's who utilize martial arts types of aggressive techniques.
Aside from being unrealistic (much less common) practicing against those types of techniques doesn't acclimate the student to recognizing the more commonly encountered assault methods.
As opposed to retreating, we will either motion to one (either) side, or forward. If/when we motion to one side, we will most often follow-up that motion with a forward motion.
Motioning forward has numerous advantages, initially it changes the distancing that the aggressor had initially planned for. It also allows the defender to apply the necessary counter-measures to neutralize the aggressor faster (than retreating, then having to move back forward in order to apply the counter measures).
Though these motions are (individually) simple forms of the taught basic motions, when combined they could (initially) be considered confusing (to the student). It's the continued practice of these motions that will simplify their use for the student.
If student's are practicing against unrealistic manners of assault, then that practice is (in fact) useless. Practicing to defend from assaults that could (most probably) only be perpetrated by a martial artist, is both unrealistic and to some degree, somewhat pointless.
For the average student, practicing to prevent the more commonly used (types of) techniques such as those listed, are of far greater benefit to those who's wishes are geared towards self-protection.