What is the benefit of changing the seed every second (or less)? Will the random numbers you get with that method differ from the random numbers you get with nevon's? I mean, will they be "more random" somehow?
I've found that changing the random seed too often /reduces/ the randomness of the numbers overall. Set it once at the beginning of the program, then leave it alone. It's fine for anything short of hardcore cryptography (but why would you be doing that in Love, anyway?).
Earliest Love2D supporter who can't Love anymore. Let me disable pixel shaders if I don't use them, dammit! Lenovo Thinkpad X60 Tablet, built like a tank. But not fancy enough for Love2D 0.10.0+.
Since an unseeded math.random() will always return the same value, this will do nothing more than what math.randomseed(os.time()) already did.
Seeding more than once in a game is not necessary (and as Taehl mentioned, it can even be destructive), unless you want predictable "random" numbers, i.e. a the same chain of numbers after the math.randomseed().
I have come here to chew bubblegum and kick ass... and I'm all out of bubblegum.