Is it ever helpful in a relationship for a partner to hide their true feelings?

This is spurred by the ongoing thread about fear and fearlessness. It seems that sometimes one partner may hide their true feelings of fear in a situation to aid their partner or kids to get through it. Another situation might be hiding feelings of attraction to a third party even though one has no plans to act on them. Is it beneficial to either partner to hide these feelings or more useful to acknowledge them?

Obviously, there is no right or wrong here. Your thoughts?