If I was an employer and I would have to select one of employees that apply, I would take a person whos long term working experience in one company in his record of service, instead of a person that has changed 8 jobs in a single year, plus he probably has something unofficial. I value loyalty more, compared to how huge professional other employee is. I see no point in teaching, giving experience to a person, that tends to change jobs often. There are persons that aim on a result, try to build a career. You cant hold them forever with bonuses, high salary, free coffee and etc.
But in general a lot depends from a person. I know a guy, who works in a company since it was created (for 20+ years), his boss treats him and everybody like crap, he is in a bad relations with the boss, many people have left that company, that guy can also quit, but he keeps working there.
This is a wrong approach, and could be the worst one that I have seen in a long time. It is not the amount of jobs a person had, but the quality of the job they do which an employer should care about, because if you can find that one worker which could do what is asked, and do it perfectly, and even take incentive to do a better job than being asked, provide higher quality results than expected, then you do everything in your power to keep that person.
The reality is that most work places offer everyone the same amount of money, and offer a promotion as a promise, and people leave because of that, if I am 10x good and someone is 1x good and we get paid the same amount of money but I have a higher chance to promote, that's not good enough. I changed 7 jobs in 4 years before I found my latest job, been with the same boss for 6 years now. Shows you how it matters to reward the worker who works hard.