Well there are pros and cons. If you have already have a queue structure set up in your environment, it may not be a good idea to have to maintain a second queue structure in the form of a bunch of local MTAs. You'll need monitoring (how many messages are queued in each local MTA?) and a way to keep those MTAs up to date.
If you just put an item in to a queue, and then have a specific cluster of machines that does nothing but grab items from that queue and push them through an email infrastructure, then it'll be a lot easier to maintain.
