When it comes to using Setups and deciding how useful it is to you and your local conditions you need to understand the definition of "Track Condition" in the Sheet.
Imo I think this is one of the biggest misunderstood/confusing statements on Setup Sheets is defining the level of grip on a given track. On most setup's from the Pro's the grip is high and few times it's medium and low. Having only a three tier scale is very broad, and I would suggest many exaggerate/overestimate their local grip levels in comparison to what the Pro's judge a level to be.
"High Grip" Setups do not work effectively on medium or low, and visa-versa. This miscalculation is why I'm guessing some people don't feel the full benefit from copying setups.
What some locals would determine medium grip for their own track, the Pro's would probably call extremely low, as it comes down to what the individual is use to (eg for the Pro's: BIRC Huge RC to Gran Canaria, & several more lower levels "our local track").
I'm not suggesting to ignore the Pro setup's (that's crazy), but encourage you to use this information wisely as some information does translate well for all conditions and classes.
hope this helps :-)