I've never really like pajamas. I feel they are kind of pricey for something you're going to sleep in. I prefer to sleep in a long camisole shirt. If it's cold, I'll wear a hoodie with it. I've been thinking of investing in a good pair of thermal tops and bottoms, since I've really been trying to save on my heat bill. But it hasn't been an issue lately since the weather is pretty warm where I am in LA.
Pajamas are useful when you prefer to buy them in sale and also if you are sharing bed with someone. I do not think there is any need for it otherwise.