A question about a recipe: Kaleidoscope of Veggies Tart

I have a question about step 1 on the recipe "Kaleidoscope of Veggies Tart" from Cheryl Warth. It says:

"Place a cooling rack over a rimmed cookie sheet. Slice all veggies into 1/4 inch thick rounds. Place on cooling rack and sprinkle with salt. Set aside for 10 minutes. This will release some of the water in the veggies." Pat the veggetables dry with a paper towel.