It's a belief that I picked up. It might be a bit contrarian but it's based on the idea that; if you don't overfeed your plants, you give them what they need in the ratios they need it, you won't have a bunch of excess that needs flushed out. You may notice that the EC of my schedule is much lower than other schedules. The second half of the belief is that you don't harvest fruits or vegetables from a dying plant (starving it to the point the foliage turns yellow) you want it to be healthy. Or, if you prefer, since bud is a flower, would you want a rose from a wilty dying plant or a thriving one.
Maybe I'm full of shit, but you asked the question so I answered. Its what I do but you can easily decide to discontinue feeding a week before harvest if you like and just give them water.