Setting the flag updates the spawner's delay which stops the spawner from trying to find a new spawn position each tick efter the event was cancelled/aborted which makes it usable for mob stackers/mergers and other plugins that don't actually want any mob to spawn in the spawner cycle but keep the overall behaviour close to vanilla.
This might slightly effect existing plugins that use this event but I doubt anyone really relied on this behaviour, the only possible use case that I can think of is cancelling the event until you find a suitable position in your plugin... and this should be handled by the plugin itself by cancelling and spawning at the position manually.
At the time this was re-added, there was concern around how the JIT
would handle the system property that enabled it.
This shouldn't be a problem, and as such we no longer need to block
access to it.
The Vanilla Method Profiler will not provide much to most users however
there is no harm in providing it as an option. For most users, the
recommended and supported method for determining performance issues with
Paper will continue to be Timings.
Adds an event to fire before an Entity is created, so that plugins that need to cancel
CreatureSpawnEvent can do so from this event instead.
Cancelling CreatureSpawnEvent rapidly causes a lot of garbage collection and CPU waste
as it's done after the Entity object has been fully created.
Mob Limiting plugins and blanket "ban this type of monster" plugins should use this event
instead and save a lot of server resources.
See: https://github.com/PaperMC/Paper/issues/917
