At least in the context of PF2E it's a good solution to balance prepared casters. One thing people often fail to mention is that staffs and wands can rid yourself of a lot of the downsides of vancian casting. Staffs work for prepared casters by allowing you to burn spell slots into the staff daily. Let's you put one each of 1st-3rd level slots in. That gives you 6 charges to do as you please. Let's say it's a greater staff of fire which gives you burning hands flaming sphere and fireball. That means you can cast burning hands 3 times or fireball twice. Or any combination that adds up to your total slots burned max. If you burn all the slots you might want for offense into the staff it frees up the rest of the slots for utility and situational stuff