from 74 Series Logic ICs regarding 74LS...
Inputs 'float' high to logic 1 if unconnected, but do not rely on this in a permanent (soldered) circuit because the inputs may pick up electrical noise. 1mA must be drawn out to hold inputs at logic 0. In a permanent circuit it is wise to connect any unused inputs to +Vs to ensure good immunity to noise.
For the 74HC.. series ( less power requirements in amount and regulation, slower ) pulling inputs is more important, I agree.