Why siths uses red lightsaber's?

Everybody knows that kyber crystals are the cause of the color of a lightsaber, and the red one's are the main color that we could see on hands of a sith, whether if it is on legends being artificial forged, or the origin on Disney's canon where they have been through the bleeding process... but the question is: Why? is there any; and if so, which is the reason of a sith's lightsaber "the need" to be red?

I mean, many of them had light side lightsabers. But then; as a dark side duelist, why would you rather to have a red one?? (besides it looks more badass) why don't you just want to keep it the crystal color it already is (in case of canon)? or why would you need to "create" a new one (in case of legends)?

do the red lightsabers have a kind of perk on sith's hands? are they more powerful??

if so and in example, would you guys think that Anakin could have beated Obi-Wan in Mustafar if he would have been using a red lightsaber???

if there's no official reason for that, what do you think about it? what are the reason would you like to be?, or what makes more sense to you?

TL:DR why is the reason for a sith to prefer a red lightsaber over a light sided one?