A practical use of this would be in helping to determine where memory utilization typically is vs. where it really needs to be and which knobs are tuned where/how.

If you wanted to run PostgreSQL in a lower memory device, such as a lower end RPi, then you might want specific features tuned down based on your real workloads. Especially if you are considering say SQLite, but aren't sure how it will perform vs. putting say half the system's resources to PG.