I?m not sure what you mean by ?useful? but will try to help with the rest of your question.
In Britain we tend to disapprove of the European fetish for collecting medal heads but, that aside, if an old buck has to be culled for genuine management reasons then his head is of technical interest as well as a permanent reminder of the hunt.
There can, occasionally, be a valid reason for shooting a mature buck with a fine head, just as long as you remember basic stockmanship and never, never, never shoot your best breeding stock.
If he?s dead, he can?t pass on his genes to another generation of gold medal heads.
Assessment of heads on the live animal is a matter of experience, which can only be acquired over time.
I would suggest you look at relevant websites such as www.basc.org.uk or www.thestalkingdirectory.co.uk, either of which will take you through the process and explain how measurement and weighing are carried out.
Trophies are measured by both size and weight, so it is important to get the skull cut right.
A trophy must also have been dried for at least 90 days before it is eligible for measurement.
If you look around Game Fairs you may find someone offering a measuring service and you can either take your own to be assessed, or just watch, learn and talk to the people concerned.