Do you need eyeshadows?
The answer is probably: NO. You also don't need many other things in your life. That doesn't mean that it will not give you joy or simply make you feel better or give you the energy to do more. Maybe a better question would be: Can eyeshadows do anything for you? And what exactly is it?
Yes, eyeshadows can definitely do something for you. And there are a few things that come to my mind in regards to "what" beside the fact that it's fun:
manipulating the appearance of the shape of your eyes
impacting the character of the look
make the colour of your eyes stand out (check out the colour theory)
Keeping in mind the basic rules of light and shadow, regardless of the colours you choose, you can achieve that. Where light (lighter shades, shimmers or anything that reflects light) will bring things forward, this area will be more pronounced and will attract more attention. Shadow will push the area back into the shadow make it more withdrawn.
close-set eyes: to make them appear further apart you can apply light on the inner corners
round eyes: you can make them seem more almond shape if you darken the waterline and have a shadow (darker colour) on the lashline
far-set eyes: you can apply shadow (darker colour) to the inner corner
What I would suggest. Play with the eyeshadows you have and dare to move further, bolder and more colourful than you believe you should. Test it when you are planning to stay at home ;)
What's the worst that can happen? If you don't like it, you wash it off...