I feel there should be dry bedding in the bed to absorb the liquid as it drains. The liquid has vitamins and sugars that will grow bacteria which is what we want to encourage. Plus food releases liquid slowly instead of a flood.

Does the water have anything in it that is beneficial to plants? Yes. But it may also have things in it that are harmful to plants. Different people have used the drainage on their plants with different results.

I do not use it for my indoor plants but I do dump it on my outdoor plants and I did see a benefit to the plants. IMHO, being in the open, the leachete got lots of oxygen and reverse the bad it contained. The plants never looked so healthy before. I didn't even dilute it, used as is but on wet soil.

I also feed watermelon but mainly the rinds as I know the there would be a lot of water drainage with the other. Instead I eat the pulp let them have the rinds.