Not really necessary, but whether to express or conceal sadness depends on the context and personal preferences, though. It's not bad expressing sadness though, especially to your closed ones because it might help to relief your emotions and burden rather than carrying those feelings alone.

Hmmm i prefer to conceal it. Expressing it openly it’s more like attention seeker (i refer to myself) so better to conceal it.

Not necessarily conceal, I think it’s good to express and to accept, but not to do it openly especially to people. At least not always since you can’t expect them to be helpful in making you feel better, some of them could even make it feel worse.

I conceal mine..

When having the feeling of sadness, its not a must that you need to open it, you have to control it so it won't affect you or others around you.

Sometimes I need to expressing it because I do need an attention. But sometimes I just wanted to keeping it by myself because I don't want disturbing others.

It's like this, some people only feel a lot better when they express their sadness openly. It might make them feel not alone in this big yet small world. And others might prefer to keep it bcos they might feel that it is not necessary for them to express it and they might be worried that it will only create trouble to other people if they express the sadness. Therefore, it depends on how people view it and how they make them feel, imo. So do I answer your question?

There's nothing wrong with expressing what you feel openly, but there's always bad and good affect. And keeping everything to yourself; trying to hide everything from other people won't give you any better, especially after a long time.