Most practical reason: because as a parent who wants a good night's sleep, it's beneficial to train your kids to sleep well also. :). (And also because good sleep habits - by which I mean being able to fall asleep in your own bed without needing elaborate rituals or snuggling with a parent - are useful for life.)
Really, I think it's mostly about getting them used to the sleeping arrangements you want to have. If they're going to bed share until six, great, let them stay. But if you have them in their own room, teach them to sleep that way.
Note that doesn't mean no snuggling and reading. It just means that when it's time for sleep, learn to sleep in your target bed.
With infants, which doesn't apply to the GP, the current recommendation is to sleep in the same room but separate bed, to minimize the chance of getting squished or suffocated.
Really, I think it's mostly about getting them used to the sleeping arrangements you want to have. If they're going to bed share until six, great, let them stay. But if you have them in their own room, teach them to sleep that way.
Note that doesn't mean no snuggling and reading. It just means that when it's time for sleep, learn to sleep in your target bed.
With infants, which doesn't apply to the GP, the current recommendation is to sleep in the same room but separate bed, to minimize the chance of getting squished or suffocated.