Changi Airport transit is a paradise.
This is why I always travel without check-in luggage so that upon arrival I can remain in the transit. If you have check-in baggage, you need to exit the immigration and pick up your luggage at the conveyer belt. You cannot return to the transit.
There are a few sleeping corners in the transit, and I always return to Singapore past midnight. I have a light supper at the transit, it's quiet and peaceful. After that, I go for a nap at the sleeping corner or try the free massage chairs. Next morning, I exit the immigration and take a bus home.