There are several disadvantages to quitting your job before you get a new one. The biggest one (in my mind) is that it is not likely that you will be able to get unemployment benefits. Depending on why you left the job it may be possible (http://www.nolo.com/legal-encyclopedia/unemployment-benefits-when-quit-32450.html). Unless you have a lot of money banked and are prepared to be bleeding your savings for a while, this is a big deal.
The second reason is that prospective employers are going to want to know why you left your old job. Saying anything negative about your ex-employer is going to make you look bad, to some extent. This is unfair, but I have heard it over and over from both recruiters and employers.
Here's an example. A few months ago I had an interview that went (I thought) extremely well. It caught me completely off guard when they called and said I wasn't going to be asked back for a second interview. I asked the HR guy for details and he was nice enough to explain. I have had a lot of jobs, working with a large variety of people. Some of them were, shall we say, challenging to work with. When I am asked “tell me about a time when you…” questions, these are the guys who surface because I am good at working with challenging people in a professional and positive manner. He told me that they had rejected me because it sounded like I was a person who didn’t get along with people, because I had so many stories about hard-to-work-with people. He told me that being positive in a job interview is very important.
Another risk in quitting your job is that you will run through your one month safety margin. After you have been out of work for a month, it starts to look bad. I have asked a number of recruiters about this, and what I seem to be hearing is that there are only two “acceptable” reasons for being out of work for more than a month. One is to take care of an ill family member. The other (and this is only the case if you have been working for more than fifteen years, so it stands to reason that you might need a break) is to “see the world”. Any other reasons will hurt your chances for employment. I have even heard that there are some employers who will round-file you out of hand if your last job ended more than a month ago. They figure if you were any good someone would have already have snatched you up.
You didn’t say what kind of work you do, but for me, in the IT industry, being out of work means my skills can start to go stale. Of course, I start out with lots of good intentions of using the time to learn new technologies and write all those programs that I keep meaning to get around to, but as time drags on and the out-of-work blues set in I find I have less and less mental “energy” and I find it very difficult to effectively learn new things under those conditions. Your results may vary.
That being said, having more time on your hands to look for another job can be an advantage if you are able to put it to good use. There is also the advantage that you won’t have to give notice at your workplace. However, IMO those advantages are small ones. Most of the time you spend job hunting is in waiting for the right job to come up or someone to call you. And I don’t often get hired by employers who want me to start right away. The wait time is shorter when I am contracting, but for FT jobs I have had “wait times” of anywhere from two weeks to three months.
Personally, I would never walk out on a job before I had a new one. But that’s just me; I tend to be a cautious person, and I don’t know how bad your job is. If it is truly so bad as to be causing you a great deal of emotional distress, then you might very well be better out of it. Attitude is a large part of interviewing well, and if you are in a job which is destructive to your attitude it might hurt your chances of finding another job.