Doesn't that favor the magic guys tremendously?
It absolutely does, in my experience. But it's also a big part of the fun -- the trick is to allow the 'magic guys' a limited, situational ability to extrapolate new, possibly clever, almost always murderous uses for their spells while reserving the right to never allow them to do it again, or to significantly nerf it.
It's the Daffy Duck school of magic. Impressive, but things tend to only work once. Nothing establishes 'precedent'. We're not playing Lawyers and Litigation. The price of loose, player-friendly rulings is the DM gets the final say on when and if the player can attempt wacky, rules-exceeding stunts.
The other necessary part of this is allowing the non-magic guys something comparable -- a reasonable chance to perform a jump off a 100 ft. tall tower on a dragon's back, for instance.
(it also helps if the non-magic guys have very high stats and favorable options on par with Unearthed Arcanas' version of Weapon Specialization)
This style does place a fairly heavy burden on the DM to be the 'last guarantor of game balance', and requires the players trust them in that role.
Like everything else fun and slightly risky, it's great until it periodically blows up in your face!