I find myself wondering if you're talking about an adjustable comb or one of those wedges built into the stock as commonly found on guns meant for the German and other continental markets?
Example of adjustable com
Example of cheek piece:
Most shooters don't see a difference in their sight picture when shooting with a cheek piece-equipped gun. This suggests that adding one wouldn't make an appreciable difference either.
My personal experience is that an adjustable comb can and does make an important difference and definitely helps position the shooter's eye to look straight down the rib/barrels. The photo example above shows an adjustable comb that I had added to one of my guns. As you can see, done by an experienced smith, it adds to the value and the function of the gun without looking cheap or out of place.
The bottom photo shows a Merkel with the German-style cheek piece. These don't actually re-position the shooter's eye to a position higher or lower than otherwise. In other words, they don't do much of anything. Most shooters report no noticeable difference when using a gun so equipped.
My experience with the German-style cheek piece was poor - they got in the way more often than they helped. I'm not a fan.
Short answer: Adjustable combs = YES. German-style cheek pieces = NO.