What makes you have to adjust the suction controls when transitioning to different floor types/pile types on a canister vacuum?

I would be sweeping the floor, I run my floor tool or power brush from a carpet to a rug and it would glue there. Then I will have to open the suction release valve up until I am able to move the floor tool or power brush. Sometimes I would not get enough suction on the ground and have to turn my canister suction knob up on the unit itself.