Have you gone from full-time to part-time hours in your job? How did you go about it and what were your reasons?

My workplace allows you to put a flexible working request in after working there for 6 months. I'm tempted to request going down to 4 days a week. I'm not a parent, nor do I have caring responsibilities. I've just decided I want more time for myself, to focus on my health, my hobbies, and I'm tempted to start a tiny crafts business. I can afford the pay cut and I'm not that bothered about progression opportunities at the moment. I also think it'll have relatively little impact on my productivity, as I'm often waiting for other people to do things before it gets to me. My work asks for a reason in order to approve the request though, and I'm not sure if saying "I can't be bothered working 5 days anymore" is going to cut it! Anyway, what's been your experience of this? Am I overlooking any downsides to going part-time?