This is an important setting and determines whether capital gains are realized when you trade between coins ex. BTC for ETH.

In almost every country such transactions are taxed so you should keep this enabled. However, there are a few exceptions to this such as France where crypto to crypto gains are not taxed. If that's the case you can disable it.

If this is toggled off, the cost basis of the original asset is transferred to the new asset (even though no gain/losses will be shown). With this setting off, assets “accumulate” unrealised gains/losses in their cost basis until sold for fiat, for example: