I asked to reduce from my full time of 35 hours (5 x 7 hours) to 30 (4 × 7.5) and my employer agreed to it. Obviously there was a financial hit, but somewhat mitigated against by losing only 5 hours rather than a full day in terms of pay - yet obviously gaining a full day in terms of days off. Plus you lose disproportionately more tax, so the loss wasn't quite as big as I thought. There's no way I'd do my job full time again, but I initially imagined I'd go back to full time if I changed job. I know now I never go back to full time though. I genuinely refer to myself as semi-retired now rather than part time, and ideally I'm moving closer to full retirement than full time work.
Mr L works full time but over 4 days. The days are long (particularly when he has to go back to a half hour commute), but he has resisted many requests to go back to 5 days