Anyone know why a drain is needed on a drip system with rockwool?

If i have 2 gallon buckets, and drip just enough solution to saturate the rockwool cube to 80%, why would I ever need drain holes? If I time it to drip twice a day, for 15 minutes, it will nearly saturate the block, but not entirely. As the plant drinks more, I feed it more. No water would ever need to drain, right?

it would be absolutely hard to be able to accurately time your drips to saturate your cubes with no runoff, you will probably come back to fint them flooded. makes more sense to make a drain back to your res

zem said:

it would be absolutely hard to be able to accurately time your drips to saturate your cubes with no runoff, you will probably come back to fint them flooded. makes more sense to make a drain back to your res

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I think I failed to mention that these would be 6x6x6 rockwool cubes. Do you think that would be easier to not over saturate considering there is so much volume in those? I appreciate your input, as you pretty much nailed my primary concern. I am really tempted to try doing it though... If by some small chance it works out, You could have a room full of 2 gallon buckets and only a single hose going in to each one, all from the same source. drain fittings on buckets are a total pia, so eliminating that would make things incredibly easy for larger grows.

isnt the drain needed to flush out your system?

im sorry thats just my opinion but i cant see it done, different plants will need different amounts of water you need to water till runoff. you can make a single drain for all your buckets by making a big vineyl or geomembrane sheet under all of them and one single drain back to the feeding res. i would never make a runoff hose for each bucket, that would look like a web of hoses below lol