I think it depends on how your baffles under the deck are spaced. For instance, my craftsman mower just has a straight open channel between the 3 blades. Installing mulching blades and blocking off the chute turns it into a great mulcher.
My massey deck on the other hand, first off I can't even find mulching blades to fit it. But even if I did, the deck design has a "bay" for each blade, and all three open up to a channel which then directs the clippings out the chute. Just blocking the chute would turn the clippings into a clumped-up mess in there. Kubota has a similar deck design, but they actually have a kit you could buy which converts the deck into a mulcher. It involves blocking off that channel I'm talking about.