It's courteous to let people know what they link is if it's 'unusual' (not a web page or image), especially when the link is visually truncated. For people on

It's courteous to let people know what they link is if it's 'unusual' (not a web page or image), especially when the link is visually truncated. For people on mobile devices, triggering a download of a large file unexpectedly is annoying and uses up a typically limited resource.