The trouble with advice is that we tend to encourage other people to do whatever happened to make us happy. You should really buy a house, my father says to me, as that made him happy. Don't quit your job during the recession, said a friend for whom job security was worth more than anything else you could put on the table. I try to remember this when people ask me about freelancing, and not just tell them to do what made me happy. I'm realising that lots of people like the idea of freelancing, but when they hear what it's really like they find it's not right for them. Here are a few points to consider:
F x S = k. The product of Freedom and Security is a constant, wrote science fiction author Larry Niven. To gain more freedom of thought or action, you have to give up some of your security. Being free to choose your work assignments means your salary will vary from month to month - significantly so. This is manageable on a practical level (savings account!) but it's probably the main deterrent against freelancing as lots of people can't bear the stress of not having a lump of cash to look forward to on the last Thursday of the month.
Claiming your worth. I know several people who are skilled enough to freelance but they just can't bring themselves to ask for money. This gets easier as you go along, but if it makes you want to go hide under a chair you may want to work in-house where someone else does this bit. See also: chasing invoices.
The value of money. Some people will make more money freelancing than they do in-house, but many will find it's a trade-off between cash and autonomy. For me, reducing my spending was a big part of enabling me to make the transition and it was absolultely worth it, but lots of people will get cold feet if you point out this could cost them their cable TV subscription.
Carrot or stick. Some freelancers rent desk space, a practice that's a mystery to me, but I understand we all have different ways to motivate ourselves to get work done. I'll sometimes lose half a day to my RSS reader (as I did in the office too) but I'll usually get on with it because I want the carrot that is building my own little business. If you need the stick, however, you may want to get yourself a boss and save the hassle.
... Lots of people want to leave work at the office and not think about it until the next morning, but freelancing probably isn't entirely compatible with that. I love switching off after a long day as much as the next person, but I have to admit I'm never really switched off, not completely. It's not my work so much as what I do, and I guess that for better or worse, that makes it a lifestyle.