Our teen currently has several recurring part-time jobs: babysitting, the occasional cat- and gecko-sitting, the rare koi pond maintenance gig and working at her church one or two times a month. The work doesn't involve an onerous amount of time and she is fortunate since she doesn't need these jobs to survive. They do, however, help her pay for clothes, entertainment and a portion of her monthly cell phone costs.
Her jobs require a level of maturity that indicate she is seen as responsible and trustworthy. But if any of them cut into study time or sleep, they would have to be dropped. School is her most important job right now.
Teens who work longer hours can suffer academically, showing less engagement and motivation, according to a study from 2007. Here's a brief abstract.
As for college admissions officers, they probably see part-time jobs as a demonstration of initiative, organizational skills and so on. But if the work gets in the way of classroom success, they just aren't worth it.