When i got mine, quite a few years ago now, (through choice, not for treatment), I decided to wear them full time from the minute I got them, just for the experience.
At first, eating was very strange as I could feel nothing in the roof of my mouth due to the coverage of the large top plate. Each time I ate anything, I was very conscious of the appliance, but that was exactly why I wanted to get them.
It was quite a few weeks before, one day I realised that I had eaten a full meal and had completely forgotten that I was wearing the retainer. Again, somehow that was what I had been looking forwards to...ie,  it was now part of me.

I have a few !
The most extreme is the activator (my avatar pic), but of course I dont wear that full time. (Cant eat with that but can drink).

The ones I wore continuously for some years were Hawley style. The the first one was extra thick and deep, front to back but then I got one with a thick bite plate which comes to the lower level of my front teeth so all biting and 'chewing' is with my bottom front teeth to the plastic bite plate. It is also slightly longer and very tight.
My molars dont touch. Interesting but fine and almost forgettable once you get used to it.
Same with speech. Speaking with it now is virtually normal and it actually helps with clarity of 's' sounds but its very difficult to speak clearly for some time if I take it out.