In the summer before my first year of college I applied for and was given a paid programming internship. In the interview, it was clear that I wasn't sure about the time commitment I would be able to make during the school year, but that during the breaks I would be able to work full time. I did work full time over that summer and during the breaks since then, but during the school quarters, I've worked only 10 hours a week.
The work environment is very fast-paced there, so it's difficult for me to be productive when I'm only there for 5 hours on two days of the week. There are two main problems. First is that every time I go in, I need to catch up on what's been done since last time I was there (and anything else I'm not up to speed on) and then work on top of that. Second, I can only work on quick and simple tasks, since I might not complete anything else in the time that I'm at work.
I've now been offered a remote job with much better pay and in a field that I am much better in than my current job. My hesitation in accepting is that I'll be burning a bridge with my current company to leave before I've had a chance to do any significant work for them.
I haven't brought up my concerns about lack of productivity to my manager because I don't think there's anything that can be changed. I simply can't work more hours and I can't do much more with the hours I am working.
I've read many of the questions here, so I know the general advice is that the employer should expect that an employee can and will leave. My manager is a very reasonable person and someone I get along with, so perhaps he would handle it well, but I'm worried that this will be unexpected.