You should treat contract transactions with the same caution that you would treat fund transfers, for the same reasons. In practice, proportionate the value of the transaction.
In all probability, a single confirmation will indicate that a transaction was accepted by the network but it would be misleading to suggest that a single confirmation is the last word.
Confirmations mitigate that doubt by the same method. More confirmations == reduced probability of reversal. Thankfully, confirmations tend to arrive reasonably quickly on Ethereum.
For clients that listen to event emitters, there is a new feature. You may receive events with a
removed property set to
true to let the listener know that a previously emitted event talked about something that is no longer part of the longest chain.
That can help the listener put its house in order and underscores that hopefully, nothing irreversible unfolded on the basis of a previously emitted event. While it is possible to "listen" to pending events, it's more common to listen to confirmed transactions, meaning the events arrive with the first confirmation. Depending on the stakes, one confirmation might not be sufficient strength of proof to move to the next step.
Hope it helps.