There I was, King Emperor Lancelin "the Bear" de Guiscard of the New Latin Empire; Sacker of Constantinople; Heir of Alexander; Norman Yokel of the Muslim world; Look Upon My Works, Ye Mighty, and Despair; fighting several wars on several fronts: to reclaim Lost Ethiopia to Christianity, to push the Bektashi fanatics out of the Arabic Peninsula, and most recently leading the crusade against the Seljuks to reclaim Georgia to the Doukases (though quite frankly he would have preferred the Bagrationis for future acquisitional reasons but what the Pope says goes right).
Having vastly overstretched my vassal limits with the newest conquistions on the Horn of Africa I was experiencing a bit of a shortage of troops, having to rely on my own levies -- always with the bureaucracy, you know how it is, someday I'll have to reform the system to be more fitting to an Empire or something -- and some devious, cunning, heretic of a Greek duke managed to compare the troop numbers of his Independence faction to mine and decided that what with my troops being reduced by and tied up with the wars his 51.000 men would easily be able to defeat my 35-ish thousand. So obviously, he declared war. And suddenly I find myself a lot less over the vassal limit.
So there, as I am pondering just how much money I am going to have to spend on mercenaries to be able to defeat these upstart little rebels, or if I will be able to defeat them at all, in walks my steward with a big stack of papers. "Oh, your majesty, I found this levy reports for 30 000 men just lying around, it seems we had forgotten them in the count somehow"
Not so tough now are you, Greekduke. But thanks for doubling my available troops by leaving my service.