Using different keys for different services is overkill most of the time.
Generally you need to have one key per host that you use (or per any storage location). You can use separate keys for separate services is if you for eg. privacy reasons don't want to associate the same identity with both services, but that's a personal choice, not something that improves security.
Generally you need to have one key per host that you use (or per any storage location). You can use separate keys for separate services is if you for eg. privacy reasons don't want to associate the same identity with both services, but that's a personal choice, not something that improves security.