There are many quirks to how this works but the unfreeze and thre length clock on enable are the most important ones.
For more information on these options check https://github.com/retrio/gb-test-roms/blob/master/dmg_sound/source/03-trigger.s.

We're currently in the 02-len ctr.s test.

Test for test_blargg_instr_timing.

This allows background to take precedence over objects.
This completes the CGB ACID 2 test compliance.

There may be a performance impact involved.