If it is sufficient that the app simply never gets to see a malformed byte sequence (or anything following a malformed character) when reading from a source that is expected to be utf8, you're right -- better to handle it via the ":encoding(utf8)" layer in PerlIO.

But if there's any need to diagnose the nature of the malformedness, or to recover any amount of usable data following a bad byte sequence within a given input record, then the extra steps involving "decode('utf8',$string,...)" are the only way to do that, I think.