Process Lasso improves performance by lowering the priorities of background processes. Other similar programs would attempt to raise the priority of the foreground process, which could lead to CPU lockups. Process Lasso itself uses very little CPU usage, and even less if you close the GUI completely. It has a service which does all the detecting and priority setting.
Process Lasso's UI appears to be a little techie-like. And it is, for those users who want to see what's going on. But, you don't need to use this at all - Process Lasso can do its work without having to click a button. In other words - you can close this geeky window without fear of shutting down the program.
As you use your computer, Process Lasso will quickly restrain a program if it decides to eat up the CPU. It is reset back to its original priority when it no longer is attempting to hog up all the processor. That's all there is to it - it is pretty much a set-it-and-forget-it type program
I use Process Lasso and recommend it. Even still, I have lockups, as Process Lasso can't do too much to processes. Nonetheless, Process Lasso helps Windows organize its processes, leading to better system performance overall.
P.S. The only surefire way to restrain a program is by terminating it. However, we can't do this to essential processes, and we don't want our browser window closed just because we switched to Microsoft Word.