I co-sleep with DD because it makes night time feeds easier and I don't have to get up so I get more rest. I did the same with DS. Then when his night feeds dropped off he slept in his cot next to my bed which I still consider as co-sleeping. Then when he was sleeping through the night we moved his cot back into his own room.

The night time snuggles are nice

ETA: I've also heard that SAFE co-sleeping can help reduce risk of SIDS.