Question time - The Byzantine's lost Crete in 825, Sicily in 827, some of Southern Italy in early 800s as well, what would have been the short term impact on the Empire until say, the early 900s?
Less piracy means a stronger economic situation for the Empire, for one thing. And Sicily in particular was a wealthy area, so you've increased the Empire's economy by keeping it.
Byzantium with territory in Italy also retains a finger on the Papal pulse, which will have major repercussions.