There are many reasons why a supporter might prefer to mail a check rather than pay online. If that's the case, you can always use Givebutter's Offline Donations features to track them and send a tax receipt. However, this used to only be available through the dashboard.
Now, with Givebutter's new "Mail a check" feature, you can enable a button so that supporters can choose this option themselves when donating. And, you can include a custom message so that folks know where to address their checks.
There are lots of use cases for incorporating a "Mail a check" button on your form, such as: