I think its a difficult one either way Op. only you can know your DS and his attitude to studying, but I do think the life skills they get are invaluable.
DS20 got a retail job in Feb of YR12, carried it on till end of A levels with no problem, picked up job in same company in spring of uni first year but then dropped it as he went into second year as it was full weekends. As he is doing a science course with a lot of contact time, he knew he would need weekends for uni work. It had, however, provided him with valuable experience for his CV and some money in his bank account.
DD, almost 18, was a different story. Less academic, she has been doing a Business BTEC and had to re-sit English Lang GCSE last year including all coursework. Last summer was her last chance to resit on old syllabus. Very stressful, and we knew she wouldn't cope with a job. She passed English, but did neglect her Business course a little - she has always been quite immature for her age which contributed to this.
She started looking for work in autumn, although I still had misgivings about her juggling work and BTEC. She managed to secure a job with large supermarket but fortunately it was xmas only.
She has also been learning to drive, struggled in passing theory, so didn't start looking for work again until recently, as she was nearing her practical. She has now been taken on by same supermarket chain as before, and passed test on Thursday. Great timing, she is independent getting there and earning some money to run a car.
I will add, we continued giving her an allowance through months when she didn't work.
All good, except she is already accepting extra shifts, when we feel she needs to give 100% to last few weeks of her Business course. Its difficult, she is not planning uni, but going to have a year out whilst she decides on next step, so wants this job to fund some volunteering, travelling, general growing up. We have been roundly told this evening to trust her, she will balance coursework and shifts. To be fair, she does have a lot of downtime in college course, not just weekends.
One thing I would say, my DS applied for year in industry jobs earlier this year. He found that interviews commonly ask for examples of teamwork, working under pressure, communications skills etc - all life skills that can be picked up from PT jobs. He asked for feedback from one unsuccessful interview, and part of it was that he didn't give enough examples of organisational skills. If someone who worked for almost 2yrs alongside A level and degree studies (and is the most organised person I know!!!) couldn't satisfy that question, then I wonder how others without any experience would fair?
My neighbour has a 19yo and 17yo, neither of which are interested in working. She is keen for eldest to work in uni summer hols, but says "I don't think he has done anything to try and get a placement or job of any kind".
You cant make them get a job if they don't want. The eldest is very bright and has stellar grades, but I do wonder what his CV will look like when he too is applying for a YII jobs. It is not only about high grades now. As so many other students have those, they have to be able to demonstrate other skills. We have been shocked at how few interviews DS got even for a YII, although he has got a placement in the end. I can only guess that post-grad jobs also want to see some life skills developed along the way too.