You can be limited in melding a new stat by that. You can factually overmeld and waste statpoints even on stats that are not already in the item. Although those tend to have a lot more generous caps, specially when different weapons of same IL (for example) have or not a certain stat such as critical rate (in which an IL50 weapon with no critrate would have a cap about as high as the critrate of an IL50 weapon with critrate)