Aside from the draw engine mentioned by L3repeating, a single twilight can make the difference between 1 sauron troll, 2 sauron trolls, or even the
dark lord himself. i've learned that the hard way.
Dizzy: "what's 1 more twilight!" (adds 1 more twilight.)
Opponent: (plays witch-king,
fell beast, sword, and something else terrible which costs 1 twilight.)
Dizzy: (hangs head in shame.)