I sometimes ask pilots to 'report leaving' their current level if I have issued them with a 'when ready' descent clearance. This is done for 2 reasons.
1. It gives me a nudge to transfer them.
2. On the sector I do, I have slow(ish) climbing Northbound departures that need to get through the Southbound descenders. The pilot report is useful in gauging if the level change is going to work
or whether I need to force the descent.
SD