In the US, short-codes are helpful for B2C SMS communication. US has many regulations on using a regular phone number for sending SMS via Applications and APIs.
For starters, a shortcode allows you to send 40 sms/second which is not allowed using a regular phone number.
We have tried to document some of the differences and cases when a shortcode is helpful: http://plivo.com/faq/shortcode/what-is-the-difference-betwee...
That said: I'll bite (in case anyone else reads your message and gets confused); as a user who deals with a bunch of services that send text messages (Bank of America, Equifax, AAA, Google, AT&T, UCSB, Pingdom...) I consider the ones where I get some random long number infuriating if the number isn't at least constant for me (as I can't add it to my address book), unprofessional (it would be as if someone hosted Apple's website on their Geocities account), and even "risky" (as the numbers are usually different for different carriers, and as mentioned even tend to randomly cycle, there's no reasonable way for me to know that it isn't someone playing a prank on me when I get the message; yes: SMS is somewhat spoofable, but replying to a short code, in my understanding, is not subject to those problems).