I'm following a build that said to get 4x arc gems and level them up as I play through the acts?

What's the purpose of this? It says to corrupt at lvl 20...but why?

2nd question

I have a vaal arc, should I just use this and throw away the other arcs?

http://www.pathofexile.com/forum/view-thread/1147951

This post was edited by MouseToe on Oct 30 2019 09:02pm

You put them into your gear so you level them while you play the game.
Arc gains a huge dmg boost when level 21, thats why u want a few of them to higher your chances of getting one.

Put a vaal orb on each of them once theyre level 20, and you might get a 21 that you can use on your mainlink

You must wait till its 20 to corrupt usually with 20% quality too.