It is also good when it comes to growth as from experience larger airlines within alliances find them in a position to order planes for other members in their alliance and either sell or lease cheap (but within alliance guidelines) to allow them to grow quicker.
That : if you buy me 30 TU204, I'll buy you 30 E190. And we'll switch. I'll have 60 TU204 & you'll have 60 E190 in the time needed for getting 30.(both are roughly the same price, and people flying them shall not be direct opponents)
Unthinkable outside an alliance. Borderline with the rules and the spirit, but widely practiced. Of course, useful only if you are wealthy enough for buying more planes than the seller can manufacture.
The rest, alliance cost, passengers boost, that's trinkets. Don't even look there. And replace those TU204 with MAX9 or A321neo before fuel prices kill you. Alliance partners can buy you some to hasten the replacement.....(I don't think you're currently flying TU204. It's just for the example).