I always thought that the main quality in sushi and sashimi fish is its freshness. Nope, not to people who eat a lot of sushi. The point is for the fish to be

I always thought that the main quality in sushi and sashimi fish is its freshness. Nope, not to people who eat a lot of sushi. The point is for the fish to be aged for the correct amount of time to get the correct flavour. The longer it is aged, the stronger the flavour will be, to a point where it is unpleasant. Different people will have different tastes, if you don't eat a lot of sushi, you will probably like it not as strong. The restaurant wants the fish as fresh as possible, so it has the most control over the ageing process. There are types of seafood best eaten fresh, and there might be some sushi I'm not aware of like that, but almost always it needs to be aged properly.