If your speaker placement is "ideal," you should have no need of delay settings. No?
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"Perfect" implies that all the speakers are equidistant from your ears. The delay is only important if they are not. The delay compensates for any difference in distance so that the sound reaches your ears at the precise moment from all the speakers. I also think that with movies it is harder to hear the difference than with multi-channel music.
My experience has been that the use of delay is particularly important for subwoofers, to minimize the potential cancellation of the sub's output with that of the FL and FR speakers.
For a simple demonstration of this, you can use a SPL meter to measure the combined output of your sub and FL/FR speakers, using a test tone at the crossover frequency. As you change the distance (i.e. the delay) of the sub, you will see substantial increases/decreases in the SPL level, reflecting changes in the summation/cancellation of the sub with the mains. As Shadorne mentioned, differences of 2 feet are both measurable and audible, particularly with music.