It is all up to you, if you like to go to out to friend's houses or to the beach or out for a picnic at naptime or in the evening, Pack n' Plays are convenient to take along to keep the baby on her/his own sleeping schedule, last weekend, we went to a friend's house for dinner, we brought the Pack n' Plays, it worked great, we could have dinner and Summer just stay couple feet away.. also we use it downstairs in our house,so we do not need to move the crib:)
About how long you can use, most brands can take up to 30lb, so it is about 1 years old, maybe a couple of month more....