I use the sensitivity (or in my case, the best curve of sensitivities) that best applies to the mechanical inputs required of the game.
Different games require different sensitivities. There is no perfect sensitivity. You're not going to get the same hand movements playing Counter Strike as playing Diabotical. One requires extremely accurate acquisition and instant reactivity to very small hitboxes, the other has much more verticality, is much more movement based, with much more forgiving hitboxes etc.
Sticking to exactly one sensitivity religiously is not going to ensure you play at your optimum level, but you still need to be able to understand what sens you are using and match certain things when you have a specific purpose to. It is still very useful (imo essential) to match sensitivities accurately in different situations, you may have an approach to synchronising sens across FOV which you take for a specific purpose e.g "I am going to match velocity at centre pixel in this game because it requires a lot of recoil control and I have worked on that a lot in this other game", or "I am going to match 360 distance, because this game requires a lot of fast turning and I happen to know that I like this particular feel of orientating myself in the game world"
People who think you need to stick to one sensitivity always for every situation without any consideration are still taking advice first penned in the 90's before the more recent research into human motor control, hand-eye-coordination and mechanical aiming in general had been done which disproves those theories rather convincingly.