It depends, to some extent, on how much a person actually earns. In theory, one of the great advantages of being self-employed is that you can take as many holidays as you like, and when you like. In practice, there are lots of self-employed people who've not had a holiday for several decades because they simply can't afford a period of time without any income. (For those who run businesses which would have to continue during their absence, taking a holiday not only means losing their own pay but forking out to pay someone else to run the business in their absence).
Self-employed people also don't receive sick pay and, if the business fails, can experience problems with claiming unemployment benefit.
Further, self-employed people have no guaranteed income. (There are plenty of people running small businesses, where their staff all receive at least the statutory minimum wage, but not earning more than about �2 per hour for themself).
Of course, if things go well, a self-employed person can make a great deal more than an employee (simply because he/she gets to keep the company profits).
It's largely down to personality types. Some people like to put their savings into 'ultra-safe' bank accounts, which pay very little interest. Others would rather seek a much better return (through, perhaps, investing in the stock market) but with the risk of losing everything. The former type of person would probably be happiest with the comparative security of being an employee, while the latter might enjoy the gamble represented by self-employment.
Chris