It depends, in part, on when you arrive. Typically my family's strategy is to arrive pre rope drop, and there's no reason to use FP+ during the first couple of hours after park opening, when the lines for headliners are still reasonable. We save our FP+ for the headliners we know we'll reach during higher-crowd times of day, either just before we leave for our nap break (11am-12:30pm-ish) or just after we return to the parks, but before dinner (4pm-6pmish).
The only exception is Animal Kingdom: if we're visiting Animal Kingdom in the morning and hopping elsewhere in the evening, we don't use any FP+ at AK all, since we generally find we can do everything we want in standby with a rope drop arrival. On those days, we make the FP+ in our second (evening) park.