If you do it wrong: it's like you're chained to someone.
If you do it right: it's like having a best friend you can rely on 200% of the time. Someone is always there to listen to you, to help you, and to comfort you. Trick is, you're always there for them as well, but the cool part is: you don't mind it. You like spending time with them and they like it with you. You have something that clicks with the other person, and you just share an amazing bond.
There are good times and bad times in every relationship. And, sometimes you get on each other's nerves. This is not the kind of 'go out to dinner on friday night' dating, but the 'dating' that is a long term relationship. These type of situations are usually more like unofficial marriages. Some end happily, others don't. The 'dating' as in 'going out on dates' is probably a lot more carefree and fun. But the longterm relationship is the best as you can grow with the other person and fall in love with them more and more as time goes along. Even if it doesn't work out, there are no regrets as you explored love to the fullest.