It happens with almost every consultation I do. We start talking days and times for the client's photo shoot and somewhere in that conversation the client will say something like, "How about noon?" The sentence makes me cringe. For some reason it always seems easiest time, but it is the worst light during the entire day.
Shooting at noon means the sun is directly overhead. There is no direct light coming from any angle but the top of your subject which often results in harsh shadows and a dead look in the eyes. The sparkle that we love in eyes so much comes from light hitting the eye, so when the light is over head and can't hit the eye, we lose those catch lights that make the eyes of your subject look alive. Let me show you what I mean.
This first image is one of my daughter that I took while we were on an outside walk about 1 in the afternoon. First of all, it is hot, so her face is red. Second, notice the harsh shadows on the different parts of her face and thirdly, look at her eyes. They look like black dots, not the gorgeous baby blues they really are.
Honestly, I prefer shooting at dusk every time. The light is beautiful and who doesn't love a pretty sunset?