I always understood the side project thing as a way to develop skills that you don't develop at work. I'm never really going to improve writing simple python stuffor crud. I have no reason to get better once I'm at the point completing my job satisfactorily or even have opportunities to get out of my comfort zone as far as programing goes. I have no way of knowing what I don't know.

When I was working on side stuff all the time, I was getting better rapidly, finding new ideas, solving problems in better ways and just always out of my comfort zone. I stopped because I did get burned out a bit. The focus was never resume filler though.