This is what kittens are when they are all sleeping together in one big lump. Until, inevitably one of them wakes up, yawns its ridiculously pink mouth, and then proceeds to step on its brother's and sister's heads in order to get at something more stimulating, ending the Golden Age of kitten napping.
This is what you want to be when it's about 6:30pm the day after you stayed up until 7am and had to work at 8am. You are suffering from sleep deprivation. All you can think is mmm... sleep. You want to take a nap, but naps are cold and alone and dark. Everyone else is up doing things while you're asleep. You wake up Groggy and Crabby two hours later than you intended, too warm, drenched in sweat with strange markings all over your skin because who would ever sleep in jeans under normal circumstances? And then of course, if you can manage to wake up enough to function as a normal human being, it's impossible to get to sleep again when you actually want to go to bed and your sleep schedule is irreparably messed up for the next three days.
Now imagine this: if instead of taking naps like normal people when you are tired in the evening, you could turn into a pile of wonderfully cuddly kittens. Kittens don't wear jeans. Kittens don't drool. Kittens don't oversleep. Kittens don't have jobs to go to in the morning. Kittens don't mind having their head stepped on by other kittens. Kittens don't get crabby. Piles of kittens are not lonely. Piles of kittens are warm in a fuzzy sort of way, not a Sweaty uncomfortable sort of way. Piles of kittens don't miss out on anything because they are always the center of the universe. Most importantly, the main function of a pile of kittens is to take naps.
Note: this all applies in basically the same way to dog people, exchanging "puppy" for "kitten". And with a little less fuzziness in general.