We found that we needed one once we bought a house because banks like you to sign + email stuff, for reasons that are unclear to me. One the one hand, the iOS "scribble on the PDF with your finger" feature has almost replaced that. On the other hand, their notes app includes a good enough document scanner, so we often print, fill out, scan and file instead of just scribbling on the PDF. (We used to print, fill out, and then use a full-duplex hardware document scanner, which provided better / faster scans, but does not fit in my pocket).