The Purpose of Scrap Iron
It is very simple. Scrap Iron can be used to repair and also heighten the level of your farming tools. By doing so, you will also decrease RP usage of the item, leaving so much more for some dungeon crawling in the morning.
Using the scrap iron recipes in your forge is also an excellent method for improving your forging skill. It's worthwhile to stockpile scrap iron so that you can use it when you're ready to upgrade your equipment.
Scrap Iron is also a simple gift (you can give away all your LV1 Scrap Iron to free up space in your inventory/storage) which will raise your FP with Ganesha . However, Scrap Iron is disliked by Kross (he will think you see him as scrap and worthless).