Long-running, total masking — playing a sound loud enough to completely cover your tinnitus all day — is now generally advised against. The reason is habituation. Habituation is the brain's natural process of de-prioritising a constant, non-threatening signal. If you remove the signal entirely with masking, the brain never gets a chance to learn to ignore it. Stop the masking and the tinnitus is just as loud as before.
Partial masking, by contrast, is fine. The aim is for the masker to sit at or just below the tinnitus, giving your auditory system something else to track, but still letting the tinnitus through. That blend is what allows the brain to slowly file the sound away.
For acute distress — a flare-up, a hard evening, a noisy day — short bursts of stronger masking are absolutely fine and often what you need to get through. The danger is making total masking your everyday default for years on end. Practically: use a fan or rain at a level just below the ringing. Save total masking for the worst moments.