Like Robert suggested (Robert's always right ), Muscle Memory isn't really designed to help your Pug. It's supposed to help your mage classes. So you can have your points put into Strength for Pug, plug in Muscle Memory, and quickly become a more effective mage.

Mages have similar Traits that benefit melee classes, so they'll convert (for example) 5 points of intelligence to 5 points of strength (or whatever). The idea appears to be to encourage players to level all classes, if they want.

Keep in mind that there appear to be caps for stat points per level. So if you're a level 40 Pug and you've got 120 points in Strength, when you switch to your level 20 Conjurer, you (apparently) only get the benefit from 76 of those points. (Here's a chart of what the stat cap appears to be for each rank. Link in text.) So when you switch to lower level jobs, it's beneficial to equip stuff like Muscle Memory, which will take points out of Strength (where you're capped anyway) and put them into some other attribute, where you can get the benefit from the increased attribute.

Have fun!