Its nice achievement.
- If you master it you can get there quickly.
- If you master staying there for long. Your mind and body will benefit like a deep sleep. i.e your mental and physical health will improve.
- and as you rightly said you get joy. its a pure entertainment.
However There is danger there
It has nothing to do with buddha teaching,or nibbana.
You master the art of retreating when your mind is disturbed. Instead of doing observation of what arised and why it arisen, what is danger in what is arising, and how to escape from what is arising, and how long it will stay. You turn your attention away from this vipasana and turn toward the joy of breathing. So whatever has arisen will get suppressed. and stay with you always. and there is no more probability of arising something else too.
The joy that is arised due to seclusion from 6 sense thoughts. is also of anicca nature, its not in your control, it arises on its own, stay and goes away. you should also see danger, escape even in that joy.
You are also wasting time, since you are not doing vipassana of thought or that joy. people can stay in this state for days. and at the end its nothing but entertainment. it is one kind of sensual pleasure only. as long as 6 Sense are there even this joy is sensual joy. A joy by seclusion of sensual pleasure is also sensual joy.