- You usually have to commute to an office every day. This requires transport and time. Freelancers usually work from home at least part of the time. Transport and time both cost money.
- You usually have social obligations around lunch with your colleagues, and can't just graze from the fridge. For my last permanent job, I worked out this cost me around $50 a week. Not including beers with colleagues after work (which is a perk rather than a cost).
- Putting up with work shit causes mental stress. One of the ways of dealing with this stress is buying stuff. I always spend more on random stuff when employed rather than freelancing. Also, the income insecurity when freelancing triggers my "must be frugal" instincts and I just spend less money.