I'm not a fan because it conflicts with grades. I have seen too many people put too much effort into entry-level clinical jobs, and then end up destroying their GPAs as a result. Then they say bye bye to medical school, and other potentially high-paying career options as well down the road. These jobs are dime a dozen. They won't set you apart.
Medical school also starts you at step zero. I volunteered in the ED, and never touched a patient. When I started my MS-1 clinical skills class, I didn't feel behind, and people with clinical job experience weren't far ahead either.
I like to compare these jobs to trying to become an airline pilot. If you want to be an airline pilot, you can become a baggage handler. Sure, you'll see the airport, see the inside of a plane, and even go into the cockpit. You'll see the environment, but you will never end up doing anything that remotely has to do with being a pilot. Same with these jobs. As a resident now, I do not do any of these tasks that are done by CNAs and etc. I'm not saying this to be an ass or to try and act superior. I'm saying this because everyone has very specific job duties.
Your best bet is clinical volunteering. It's once a week with minimal impact on grades, and will cover all your bases.
For the naysayers that tell me how amazing these jobs are, I'll say that I'm not discounting your experiences and the wonderful encounters you had. But as a physician, you have the REST OF YOUR LIFE to have these experiences. You only have a small window to get into medical school.