Recently I've taken a liking for sweatpants. I actually think that they flatter my shape when paired with a very slim fitting shirt. I have very small hips/legs with a broad upper body. The slim fit shirt emphasizes my waist while the sweatpants make my lower body look bigger, thus balancing and flattering my shape.
Loose or baggy sweatpants should always be worn with a body-hugging shirt, otherwise they look sloppy.
I also think the shoe is important. I haven't seen anybody able to pull off sweatpants with flip flops or Uggs yet without looking like a slob. A slim fitting pair of shoes like Keds or Vans or even a pair of flats should balance out the bagginess of the sweats well.
I don't think it does. Everyone has lazy days or days when they can't be bothered to impress people. I like wearing my boyfriend's sweatpants/joggers. I'm wearing joggers now, I usually wear them when I'm lounging around, skinny jeans aren't comfy to laze in!
I love sweatpants for the same reasons that every girl has mentioned - they are super comfy. I actually love to wear sweatpants or PJ bottoms when ever I am at home! they can also be sexy if you wear them with the right tops.
I only wear sweatpants in public when I am feeling gross and unattractive (usually because I am on my period and I am bloated and stuff) so when I see other girls in sweatpants I usually assume she is on her period.