Apologies to those who have been on this merry-go-round long enough to be sick of hearing this, but...

How important would you say physical descriptions are when it comes to characters? I appreciate in some cases alluding to certain physical traits might be essential. For example, your protagonist might need to have black skin in order for your story to make sense (and just telling us where that person hailed from may not be enough to convey that particular attribute). But, I'm thinking in a more general sense when it comes to keeping readers engaged with fleshed out characters. Do they really care if character A is short, tall, heavy, skinny, has brown eyes, etc, if this is not directly relevant to the story? Can they not fill these in with their imagination?