The purpose of valor is to help people get specific drops they need, as they can get them at any ilvl and then upgrade them from there.
It’s generally used for trinkets.
Using myself as an example, the best tanking trinket in the game is off of Hakkar in De Other Side. I’ve done De Other Side almost 30 times in M+ and have never seen it drop, even when I bring 4 friends along with tank loot specs to help me try and get it.
But we’ve also been killing Hakkar on M-0 every week (since M-0 bosses have individual loot tables) and was finally able to get the trinket a couple weeks ago, that way. And now I can upgrade it to 220.
The purpose of Valor is to free people up to farm for the item they need on any difficulty, since they can then just upgrade it to a respectable ilvl. Instead of having to rely just on RNG from the Great Vault to get the item up that high.