the difference between counters and instantaneous levels

Measure resource usage.

Count times allocated and times released.

If you measure them both at the same point, the difference should be the resources in use at that point.

But gives extra info - the rate at which resources are being used.

Assuming discrete sampling, some stats aren't available: eg peak resources in use in a particular time period (because there could be a massive spike in both counters between samples, but you have no idea if that is because there were a million allocate/release samples, or if there were a million allocates then a million releases)