You can sell your yellow gold for cash. There are a few quests that require certain kinds of gold chunks, but for the majority of the time, it is completely safe to sell any and all of your regular YELLOW gold. NOW - the big exception to this is WHITE gold and Trigold nuggets. These are rare(ish) and need to be used for some tasks. Keep a safety net of them around at all times. The other way to get yellow gold fast is to turn in wooden sets, they will net you one 100 ounce nugget and one nesting box. You can then sell the yellow nugget as above.