As I am often heard saying, "compression is the Holy Grail". When your engine is putting out the maximum compression pressure it can, and in spite of that you're running slow, rings and valves can pretty much be eliminated as a cause. And a compression check is so easy.
You check the compression after break-in. The first thing you check, when you get back to the shop after a race, is the compression. If it hasn't changed since the last time you checked it, or has maybe gone up, it would tell you that the rings and valves are still in good shape. If it has gone down, since the last time you checked it, that would indicate a problem. This is where a leak down test could come in handy. It would tell you if it's the rings or valves are causing the drop in compression pressure.
With my two cycles, if our times were slow, the first thing we would check would be the compression pressure. It's not the end-all for tuning, but it definitely has its place.
If you find your lap times getting worse, a compression check is a fast, easy and convenient way to eliminate one possible cause.
As far as the compression release is concerned, it doesn't eliminate compression, it only lowers it. The fact that a modified engine may or may not show more or less compression pressure means nothing! If your engine makes a certain amount of compression pressure, whatever that amount is, that is your base number to compare subsequent readings to.