The really nice thing about using verdata is that you can use it freely, without needing to worry at all about screwing up your players' UO files; since EA doesn't use it, you won't ever be overwriting something that will screw up what players need to still play OSI, or other shards.
Of course, it's just as easy to get that effect by hex-editing a custom-named client, and providing custom-named files as well. Then again, some use UOGateway, and make this whole discussion moot.
All of that said, though; I don't see how using verdata or not makes patches smaller or larger; If you a truly 'patching' the files, it wouldn't make any difference at all. (except if you are one of the shards out there forcing players to patch/over-write their default UO files, shame on you!

)... on the other hand, if you are providing the ENTIRE files that you are changing to be downloaded, the verdata method is much, much, much SMALLER in size (if you do it right, and if you don't have a verdata that has been packed with hundreds of megabytes of junk).