For prints, Leon is spot on. Some years ago, I turned my third bedroom / box room into a darkroom and spent ages getting it virtually 100% light-tight. However, by default, I also produced an almost 100% hermetically sealed room where ventillation / air flow was almost non-existant and heat and humidity achieved levels capable of growing tomatoes.
I did away with the draught excluders which "protected" the paper against stray light coming under the door from the hallway and never had any problems.
As I always used a changing bag and drum combo for developing film, I can't comment on if / or how much of a problem a little light is for film but my guess is that, as it's a load more sensitive than paper, complete darkness is a necessity.