I guess that adds some additional legal protection in case there is some dispute in court (e.g, the court may believe you that you always sign via HelloSign and

I guess that adds some additional legal protection in case there is some dispute in court (e.g, the court may believe you that you always sign via HelloSign and that HelloSign is sufficiently trustworthy to trust that absence of a audit trail means that it was not you who signed the document). It is probably still easy to forge things, after all, you yourself may also be signing documents without HelloSign sometimes, but I don't think that is much of a problem. It has never been all that hard to forge signatures, so in the end it comes down whether you can actually make a court believe that you signed the document or not.