PT has no adverse affect on the normal 'running' speed of your computer - it doesn't install any services or leave anything running in the background. When you exit the program, it shuts down completely and cleanly. Leave both programs installed.
Of course, the purpose of the program is to optimize your PC, so after you run a few of the utilities, you will find your computer running smoother and more quickly. I have a 7 year old AMD-powered desktop that, literally, runs more quickly and dependably than the day I got it, primarily because of Power Tools. I've tried almost all of these kinds of utilities and NOTHING is better than PT!
Have fun!