Sometimes it's about wanting a trivially shorter keyword.

!h searches Hoogle; I would prefer it to search Hacker News. To search Hacker News I have to use !hnsearch or !hn

!hn isn't much larger than !h but is still something I would prefer to set myself.

!m goes to Google Maps but I would prefer to use another map service. I could use !mapquest but would rather it just be !m

!sd goes to Slickdeals instead of Science Daily (which is !sciencedaily , talk about lengthy)

E:

I just compared my keywords and then searched the DDG Bang list for where I would be taken if I had used DDG instead of ones I set myself.

E:

>Plus I make ddg my default browser so I do just go to the address bar put `!yt cats` and get youtube cat videos.

I just type "y cats" and get youtube cat videos. ;)