You can create your own mpq with any mpq editor and then use MPQDraft to create your own .exe that also laods the mpq.
The only purpose imo is so u can work around the 8mb limit in Multiplayer.
The exe then also laods the custom MPQ, paths gotta be correct n Stuff.
Everybody who wants to play the map also has to have wc3 started with that .exe.
Then you can host in B.net.
Only Mod i know that (will) uses this is "the power of fire" from Barade.
Other way with no MPQ is that you put your resources into one directory eg C:\\Program Files\Warcraft III\Maps\MyMap\Data\Models\Peasant.mdx and in the object editor you set model path to Maps\MyMap\Data\Models\Peasant.mdx. You can do this with everything from icons to skins, sounds... But you have to install warcraft properly or edit your registry. With this you can use local files on your disk however playing it on Bnet is not so easy because other players has to have files too. Like frotty's way just you don't need any exe.