I have spacers on my car 12 mm front, for one reason only. Coilover strut housing does not clear stock front wheels regardless of height adjustment.
As long as you use quality spacers (rogue engineering makes good hubcentric) you should have no problems. Over time though, your wheel bearings will probably have somewhat reduced life and different track front to rear will play games if you are trying to dial in oversteer/understeer.
If you have a choice avoid them, but if you must, try to get something less than 10mm preferably.