Not if you're like me who's hovering at the low end of normal BMI anyway. Gaining weight isn't easy for everyone.
Posture is positively affected by lifting too. You need to do something to balance muscular development through your body, it doesn't need to be lifting.
If you don't do physical exercise losing body fat will mostly make you look skinny, not muscular.
you won't loose your disgusting gunt otherwise.
It's a fact. I see a lot of "work out" men that are unbelievable obese. Something 75 years ago would be circus material. They might have strength, but optically it is just not esthetically.