The fused disconnect acts as (or like) an additional service disconnect, it has overcurrent protection. It is necessary given the supply side connection shown in the diagram.
The unfused utility disconnect to the right is labeled utility disconnect. It should not be necessary in this diagram unless the fused disconnect somehow doesn't meet the utility's requirements for a disconnect. For example if the fused disconnect were inside and the utility wanted their disconnect outside. Some people seem to think that an NEC-required disconnect cannot also serve as the utility-required disconnect, but in my experience that is not true if the disconnect satisfies both requirements. Not all utilities require a bladed disconnect. That is not in the NEC. But it's a common utility interconnection requirement.
Supposing you were able to connect to the panelboard with a circuit breaker (load side connection instead of using a supply side connection) the unfused utility disconnect might still be required by the utility, but the fused disconnect would not be. There's lots of threads here on the rules for load side connections, trying looking at a few. You at least need to confirm the busbar rating in the panelboard if you want more feedback on that.
