Yeah, see, that's what I've always thought would be the most efficient approach. But I've seen cases where it basically ends up in a clusterfuck ala;

Player 1: I prep my kamehameha.
Player 2: Oh shit, I quickly fire a bunch of ki-blasts to stop him from charging his kamehameha!
Player 1: I fire my prepped kamehameha, destroying all the ki-blasts on it's way over to Player 2.
Player 2: I die horribly!

Or;

Player 1: I prep my thunderpunch.
Player 2: Oh shit! I try to punch him to stop him from charging his thunderpunch!
Player 1: I use my prepped thunderpunch towards his face, meeting his fist along the way.
Player 2: I die!