If someone gives you split coins and you spend those coins in a transaction that includes your other coins as inputs and give the rest back to yourself as change (the default behavior of every wallet), then all of your spent coins are now split. Whichever side they are split on, your coins now only have value on that chain. If that chain dies, then your money dies with it.
It is possible for a nefarious actor to attack the network by sending split dust to every wallet. What looks like free money is actually poison causing your wallet to follow one chain. Most users will have no idea what is going on in the hash battle and will not realize that by merely spending free dust that they lose all of their money.
It is important for any wallet software that operates during the hash battle to have a policy about split transactions. There are two safe options. The first option is to not create transactions during the hash battle. This is undesirable and obviously impacts all economic activity negatively. Fortunately, there is a second option: wallets can transact safely during the hash battle by following the anti-split procedure.
The basic idea of the anti-split procedure is for wallet software to run both nodes (ABC and SV) and mark any transaction not valid on both nodes as “split”. Split transactions are poisonous during the hash battle and are to be held in stasis and not spent. After the hash battle is over, any split coins on the winning chain are removed from stasis and can be spent. This procedure ensures users are able to transact safely during the hash battle without risk of funds loss.
It is not sufficient to run one node. Wallets that run an ABC node exclusively will receive DSV transactions (and all descendants) that will be lost if ABC loses. Wallets that run an SV node exclusively will receive MUL transactions (and all descendants) that will be lost if SV loses. It is important to validate all transactions against both nodes simultaneously to ensure correct categorization of split transactions.
There are five apps committed to following the anti-split procedure: Money Button, Yours.org, memo.cash, matter.cash, and CoinText. If it is not clear whether your wallet supports the anti-split procedure, then your best option is to not transact until the hash battle is over.
Are you the author of wallet software? Join us in the Switzerland of Bitcoin Cash by adopting the anti-split procedure.