You don't want to create any horizontal lines in a room with low ceilings. You didn't specify what type of moulding but definitely no crown or chair rail mouldings.

typo on moulding . Thanks for the advice.

Depends on the house--can you post photos? There are old homes from the 1700s with 7' ceilings that have moldings, but yours may not be one of them. I think if you installed a 3"crown molding and a 7" base molding, and painted all the trim and drywall the same color, it wouldn't chop up the room and make it feel more spacious.

There's a lot of molding here, but it looks all of a piece since it's all the same color:

FWIW, we have 8’ ceilings with crown molding. When we moved in two of the bedrooms didn’t have any. We had molding installed and it immediately ”raised” the ceiling by pulling the eyes up. Walls and ceiling are the same color. I agree with Diana; it just depends on the house.