I went freelance cause I had a client offer to hire me contract (vs through the company I was working for at the time). It worked great for that (I was freelance 7 years), but now that I'm in a job again, it'd take a lot to get me to go all freelance again.
Positives:
Flexible work schedule, no conflicts of interest (everyone knows you're working with multiple companies), freedom over your own job and company (hire an assistant and charge the same rate!); there's freedom to turn down a gig or client if you don't want to do it (if business is good.) You control your destiny.
Negative:
You become your own accountant, sales person, HR, assistant, etc etc, and all of those duties are unpaid.
I felt constantly on-call - It took years for the fear to go away that I could go away for a week and wouldn't lose work. Clients deadlines had to come first, so I missed important events, birthdays, etc.
When work was slow, it was stressful. It sounds great to work 4 days a week or have 2 unexpected weeks off when you're employed... when you're freelance, your eye is always on the bank account.
Individual health care plans suck (in the US).
It's tough to have the diligence to invest when you're freelance (especially if you have business expenses)
In my field, it's normal for people to go back and forth to freelance. I don't have it as 10 line items for each of my contract jobs - just the name of my own company (with a time overlap with the old job).
In retrospect... I wouldn't go freelance just to have control over myself or a company. I'd do it cause it's going to open up doors in your career (that you can't get elsewhere) and I'd do it for a big pay bump. I'd also do it if I had a good nest egg already in savings. A colleague used to call it a "f**k you fund". If you don't have a good buffer, then you get stuck saying yes to crappy clients sometimes just to pay the bills. It's nice to have a little freedom to say no (to the bad ones).