Many summoners still don't know the existence of the rune combiner. Even in pro players' guides nothing is mentioned about this tool. Is it really that useless?
The rune combiner is basically a simple tool located on the bottom right corner of your rune pages. Just click on the recycle button and there you go! So what does it do? It simply takes 2 or more runes and combines them into one rune of the same or higher value. But still how can this tool be proven useful?
Well first of all, on your pre 20s you may have done the completely useless thing of getting Tier 1 or Tier 2 runes. It was a total waste of ip my fellow summoners but it's ok. With the combiner, you are given the chance to sacrifice five of those useless runes for a tier 3 one! The tier 3 that you'll get will be random, but there is a high chance that you will need it in at least one of your builds.
The other reason why you could use the combiner is, if for example you bought some wrong Tier 3 runes by misclicking or you don't need some anymore, or even because you got some useless ones out of the combiner. Then feel free to combine them(you need to sacrifice 2 Tier 3 runes for a new rune of the same value). Some time the combiner can save you some ip, or if you get some runes of the same type out of it, you may get inspired of creating a new rune page.
That's all there is on the rune combiner. Can be useful some times but generally if you know your stuff you are gonna find yourself using it rarely. WHATEVER YOU DO, DO NOT SACRIFICE THE TIER 3 RUNES THAT YOU USE AND YOU ARE HAPPY WITH.