I'm a side projects type guy, but maybe one downside of having active side projects is that it might interfere with work? As in stealing mental capacity and wanting to go home to work on your current side project
This has happened to me sometimes.
It depends on how much time you spend on side projects I guess. It also helps for me to have a fixed work schedule.
Having inactive side projects (as in never started, or a tiny bit ages ago) interferes at least 'emotionally' for me. Sometimes I can't stop thinking about an idea I want to work on, excited to 'go home' (i.e. stop working) and work on it, but then by the end of the day I'm too tired, if not physically then of sitting or computers, and cook, eat, and sleep instead.
For a while indoor 'cycling home' as I did when I went into an office more worked well to delineate the day, shower, and get on with something of my own feeling refreshed. I still do it, but I suppose I'm used to the feeling or whatever, I don't really find the same benefit any more.
This has happened to me sometimes.
It depends on how much time you spend on side projects I guess. It also helps for me to have a fixed work schedule.