Post-processing, which I assume is what you mean, is pretty important. Lightroom and a slew of similar programs can help immensely in cleaning up good photos and saving otherwise unusable ones.
Basic stuff like brightness, contrast, saturation, and levels/curves can change the colors and exposure of a photo in a lot of ways to get you to what you want out of a shot.
Photoshop can do all of the above, but it's also got way more features when it comes to compositing images together like 'photoshopping' heads onto different bodies and similar Digital Art nonsense.
tl;dr LR and PS are both good for post-processing. PS has more features, but LR has a way better batch editing.