Moderate recoil keeps the gun steady and lets you see the impact, which speeds up learning considerably. You correct immediately, you understand the effect of a change of position, and you work on consistency rather than on absorbing a jolt.
The cost per shot is lower, which matters when you start: progress comes from volume, and an affordable caliber lets you shoot more. The noise is also less punishing, which helps you avoid flinching in anticipation.
Its limits are well known: the .22 LR forgives some sloppy grip, and moving to 9 mm requires readjusting. That is not a flaw, it is simply a stage.
The 9 mm forces you to master your grip, your alignment and your breathing: recoil exposes position faults immediately. It is demanding, sometimes frustrating at first, but highly instructive for anyone who wants to progress across more varied distances and cadences.
It also needs the right environment: a range that allows it, serious hearing protection and enough regularity of practice not to start from scratch every session. Without that, the caliber becomes a brake rather than an engine.