Coins have these major advantages:
Weight and fineness are always a known quantity. That makes coins much easier to buy and sell. Numismatic (collector) value is a bonus.
Gold jewelry is harder to evaluate. In buying gold jewelry, you are paying for workmanship, and you are unlikely to get that back when selling (Cash4gold.com and similar outfits give you nothing for workmanship or precious stones that may be part of the piece).

Jewelery you can wear, it’s value is based on the gold content 10kt, 14kt etc. And the stones, diamonds, emeralds etc. And the quality of those stones.

Coins are always a higher percentage of gold. You can’t wear them.