Gnomish:

The thing is, that without pressuring people to claim, we have no information at all. At least with it we can learn something about the player, whether or not they tell the truth, through the nature of their claim. What alternative means of gathering information do you propose?

A more in-depth explanation:

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Take one player, who for clarity will be known as Lynette, and assume that she's a wolf who has has seven votes on her, out of ten that it would take for a lynch.

Lynette then claims as the Diviner, and either says can scry or has someone assume that she can due to the role's name. If she says that she can scry, the town can then ask who her targets have been, and if not, they can ask what her power actually is, and how that relates to her role name.

Assume that she claims to be a seer. An already-scried list of only dead players is somewhat suspicious, if she gives one, but unlike in most games it can be tested, since, unless she's the Grave Digger, she can't be sure that whatever roles she claims to have scried them as are wrong, which will lead to counterclaims from whoever actually does hold that role.

And, eventually, she'll have to scry a living person, which, since she doesn't know the other wolves, she can't have arranged with them beforehand, meaning that there's a fair chance of her being wrong, and thus it being revealed that she lied about her role when whoever actually does have it reveals their role and/or the person they claim to have scried says they're wrong.

The same holds true for most powers ("You're a silencer? Oh, alright then. Silence someone!", etc.).