The one advantage of vassalising is that it lets you send a raiding half stack army off on a rampage through enemy territory - by vassalising you don't have to stop and get loyalty back up but can take a new province every turn (at least in the west and centre where few castles are more than one turn apart and the AI almost never remembers tto garrison them).
This worked very well for me as Oda - I had started off occupying provinces in the Owari to Suruga arc - and then I was attacked by endless stacks of Ikko Ikki - while I beat them off again and in siege battles my Owari army lost units faster than I could replace them and it was only a matter of time before they sent one stack too many.
So I scraped together a half stack of ashigaru, put them on a boat at Mikawa, landed them in Ise and then went on a rampage through Yamato, Iga and Omi vassalising each one in turn.
As it turned out that they only had those provinces plus Mino which they left undefended for one turn and Echizen which someone else took I destroyed the clan in about 5 turns without having to fight a single proper battle - every time it looked like I was going to get intercepted by an II stack I took the castle first and then it had to leave vassal territory.
In fact this sort of raid is the only safe way Oda can venture westwards in the early game - actually occupy Omi, Iga and Yamato and you'll be endlessly fighting to hold on to them.
And historically this was the grand strategy that Hideyoshi used to unite Japan - he didn't eliminate most of his rivals he just turned them into vassal states.
Bookmarks