A full diary feels like proof that the business is working. Often it is proof only that the business is busy.
Activity and progress are not the same thing
Plenty of profitable-looking work is barely profitable once you account for the time it consumes, the rework it creates and the attention it takes away from better opportunities. The pressure to keep the wheels turning makes it hard to notice.
Questions worth asking
Which work would you keep if you could only keep half of it? Which customers take the most managing for the least return? What are you doing because it earns money, and what are you doing because you have always done it?
If everything is a priority, nothing is being prioritised.
The point is not to work less. It is to make sure the effort you are already putting in is aimed at something that pays.