Not everything, but it is certainly something you should be aware of. Look at the difference in these two pictures of Red Rock Canyon, Nevada, yesterday morning:
Majorly different, no? And why? Because I took them about an hour apart. 9am (first) versus just before 10am (second). And that darn sun had shifted. See? Proof that it turns around the earth.
Both acceptable pictures (note the curves, and the other compositional elements described in Impactful Travel Photography?), but both different. See the differences?
Light really is very important and as a photographer you should always be aware of the nature of the light: where is it, how contrasty is it, how bright is it, what colour is it.