I'm kinda new to theory as in I'm using ZeGuitarist's Ultimate Guide to Guitar and I just reached the point where I can memorize about 4 out of the 7 major scale shapes but I hear everywhere that rock guitarist's don't use a lot of theory in their playing and I'm wondering if I should just be safe and vitalize all of his lessons or just certain sections because I know you need to know scales to solo and improvise but I don't see the use of chord construction for hardcore, metalcore and metal music? If somebody can explain to me how this will all tie eventually that would be great because I don't want to waste time learning stuff if I'm never going to apply it in my playing.
My Gear
-Marshall MG10CD
-Line 6 Spider 3 15 Watt
-Jackson JS30RR
-Ibanez RG2EX1

You dont need to know theory to create songs, be it metal or some other style, but I can tell you that knowing theory will help A LOT.

I mean, if you know theory, you will be able to create cool stuff much sooner. Also its great to know wtf is going on when you hear/play something.

Gogo learn theory if you have the time and patience
Theory typically will speed things up regardless of the genre, and will make explaining your song to someone else easier (believe it or not, a full tab takes a long time to make, while naming a few chords doesn't).