Payment providers will often have fees that operate as some percentage, plus some constant. If an invoice would be charged below a certain threshold, it may not be worth charging at all. It would be useful for these invoices to set a value where, if the invoice total is less than that amount, the invoice is "forgiven" and considered paid automatically.
As an example, If I have a user who uses a feature just past the free tier due to site lag on user-visable usage, or other such issues, their total usage might be under the 50 cent stripe minimum charge. In that case, its not worth charging the user that amount, and for perception reasons, it may just be better to forgive that invoice.