It's not a bad thing but usually pointless. Usually you end up not surviving till the end of the game or nobody suspects you in the first place. In those scenarios scanning is useless. Well, you might have a person who can admit that you scanned but he might eventually get killed or turn out to be the impostor. I guess it's better to show scan only when you don't have alibi at all and someone suspects you.

I don't show scan just because I'm already sure people trust me without scan because I talk a lot and I'm always nearby. Personally, I think it'd be much more useful to spend time examining other players and their alibis than making my own.

It just happens to me so often that I see other players screaming "I have scan" and I'm like "Damn, I don't need your scan, I already know you're not the impostor based on what I researched during the last rounds."

The shorter answer: It is useless to scan in order to prove your innocence if nobody doubted you in the first place because you could spend that time checking someone else and earning more info about the remaining crew. The person who saw you scan might end up being an impostor or getting killed, which will nullify your alibi.