Um. That's a very complicated question about life, the universe, and everything. There are many circumstances during which saying particular things are beneficial.

Maybe some examples would help?

You and your friend Anna (to pick a name) are having ice cream. She's talking about how she felt when her mom died. You point out in response that the atomic weight of molybdenum is 95.94. This is very unhelpful and probably should not have been said, and she's offended that you don't care about her feelings as much as she thought you did.

Now you and your friend Anna are being held at gunpoint. You are hooked up to a lie detector and asked if you think Anna looks fat in those jeans. If you lie, they shoot you both. Anna would be offended if you think she looks fat. (ETA: as it happens, you do think so.) In this case, it is probably best not to lie.

And there are various other sorts of cases as well.