does it reduce the nutritional value?
yes
Cooking of any sort will leech or destroy some of the micronutrients out of a vegetable, but as long as you don’t really overcook your food it’s probably not too big a deal. And you have to remember that cooking also improves the digestibility of many vegetables - so it’s kind of a trade-off.
Anyway, sauteeing your veggies won’t leech nearly so many (water soluble) micronutrients as boiling them.
I can only eat so much raw veggies a day, so even when I don’t have the time (or inclination) to steam some, I’ll just sprinkle a little garlic powder, imitation butter powder, and a quick spray of olive oil on some veggies, toss a sheet of plastic wrap over the bowl in the microwave, and nuke it for about a minute.
S
I like to cut up veggies into different-sized pieces so that they are not all cooked uniformly. Some are basically raw in the inside and some are borderline overcooked. I feel like I’m covering all my bases that way.