Vacation and then occasionally (like once a month, or sometimes for a stretch of several days but then not again for several months). I actually would be fine with it being more frequent, but DD mostly only wants it at bedtime— she never wakes up in the night unless she’s sick or very rarely when she has a bad dream. So she never has a reason to come to our room at night. If we cosleep when not on vacation, it’s because she’s having trouble falling asleep and one of us stays with her until she’s asleep and then just stays for comfort. Her bed is big enough that this is not uncomfortable for us.
DD is 4.