I mean people who refuse to lash themselves to one party but each election, they will evaluate the parties and vote for the one they think best.
Except surely that means they're voting for whoever will personally benefit them right now. Whereas, your voters who always vote Tory or always vote Labour, etc. are clearly thinking on a level beyond mere self-interest, right? They're accepting a whole ideology.
And yeah, the parties get in and stab them in the back, but that's a sort of side issue I wanted to gloss over. :D
But because those floating voters swing the election, it means most of the effort will go into winning them over and keeping them, which might be bad, overall.