Trial and error has taught me to rely on computers for many purchases. I wouldn't necessarily say "big" per se, but anything that requires you to do extra validation or fill out forms is just a pain to do from the phone. Glitchy things often happen because too many companies have badly coded mobile experiences.

The worst is when I try to do things on mobile where I follow a link from an email, then partway through get a "We need to verify your email address, please enter the code we just sent," which I can't get to without closing the webview that is currently being served up by my mail app and starting over.