After quitting a PhD program, would time off before applying to a new program be harmful?
A respectable wish, but perhaps not the best approach. I would suggest a few points to consider:


If you want to form an opinion about what it's like outside of academe based on one single work experience (at one company or organization), then indeed it will be a biased opinion as it will be based on a sample of 1...and you don't know if it's representative of that 'life' or is an outlier. Best case, it will be representative of only one category of jobs outside of the academe (e.g. for profit, non-profit, NGO, small, mid-size, or large orgn, in one industry or another). 
I would compare leaving the academe for the 'real world' to not dating another girl to appreciate one's girlfriend, but to hooking up with a guy to see if you like guys better than girls. I think that would be a more accurate reflection of the difference in culture, incentive structure, relationships with superiors/bosses and colleagues, compensation/quality of life, work schedule/flexibility, free time after work, etc. Or like living in a foreign country for a while. 


Is it a great learning experience even if it turns out to be a very challenging, boring, and generally unpleasant job? Absolutely. It will teach you how to work with different kinds of people, how to handle responsibilities - in other words you will become more mature and 'seasoned' for what life may bring to you at some later time. You will be better prepared to handle reality.


Leaving a PhD program before graduating is a strike against you, which may result in a vote of no-confidence from past advisors. A more mature approach would be to take a 12-month academic leave, which is perfectly 'legal' and within the boundaries of acceptable professional conduct. 


Academic leaves were designed for students whose life circumstances make continuation in a program very challenging, thus providing a way to continue in 'good standing' while taking time off in a structured way. That leave of absence may not need to be explicitly stated on your CV, it will merely postpone your graduation by a year. If employers care enough, they might ask; otherwise it will be hidden in that space on your CV between the graduation date from your Bachelor or Master's program, and the graduation date for your PhD program.


I would recommend against taking a leave of absence for more than a year (there may be a maximum cap of 12 months set by your university's graduate school policies anyway - check with them to find out for sure). 
If you do end up taking a leave (which I think is really the way to go in your case), there may be some really cool ways to spend the year other than working the 8-5 drudgery for some firm. 


There are countless graduate fellowships, community service organizations, foreign exchange programs, etc. that would be happy to have another warm body in their ranks for a year! Something like an international fellowship or community service experience could give you much broader exposure to different organizations, different kind of people, different workplace settings and cultures, than being stuck in a cubicle somewhere on the 40th floor in a concrete jugle. 

So I would cast the net broadly and see what's out there. Your university's career services office could be a great place to go for advice. 

Lastly, leaving a graduate program mid-way will mostly likely result in wasted time in terms of what it will take to re-start graduate studies and get to the same place where you are now. Not all credits might be transferred, thus some quarters or semesters that you have already spent in the program may go to waste (at least on paper). It will take renewed effort to build new relationships to secure RA/TA funding. And of course there is always a risk (which someone mentioned already) that you might not come back. A half-finished degree is really no degree, and doesn't count for much on a CV other than explaining what you've been up to for N years (though not necessarily to your credit). 

Bottom line: I would suggest to stay in the program but take academic leave for 6-12 months. Before you do, first find a solid opportunity and get accepted/admitted to it, so you know for sure you won't be fumbling for months and wasting that precious time getting something lined up.

Hope this helps. Good luck!