Depends. The main problem with having coins with similar blockchain and transaction formats means that a transaction can be valid on all of the chains. This means that if you send a coin on the BTC blockchain from a BTC address to a BTC address, you can also be sending coins on a BCH address, from a BCH address to a BCH address since the transaction is considered valid on both chains*. Resulting in merchants receiving more than what was intended.
I thought this was only a risk if using an improper client? So if I were to use a bitcoin cash wallet to send bitcoin cash, it should not send bitcoin gold by mistake, right (even if replay protection was not active)? And vice-versa.
As someone else mentioned, what about the risk that one of the forks will steal coins on the other fork? In my mind, the best procedure would have been to move coins to a new address before each fork. So if BTC were sent to a new address prior to the BCH fork, and then the BTC was sent to another new address before the BCG fork, without actually claiming any coins for either BCH or BTG.