What is the shebang/hashbang for?

Is there any other use for shebangs/hashbangs besides for making AJAX contents crawlable for Google? Or is that it?

The hash when used in a URL has existed since long before Ajax was invented.

It was originally intended as a reference to a sub-section within a page. In this context, you would, for example, have a table of contents at the top of a page, each of which would be a hash link to a section of the same page. When you click on these links, the page scrolls down (or up) to the relevant marker.

When the browser receives a URL with a hash in it, only the part of the address before the hash is sent to the server as a page request. The hash part is kept by the browser to deal with itself and scroll the page to the relevant position.

This is what the hash syntax was originally intended for, so this is the direct answer to your question. But I'll carry on a bit and explain how we got from there to where we are now...

When Ajax was invented, people started wanting to find ways to have a single page on their site, but still have links that people could click on externally to get directly to the relevant content.

Developers quickly realised that the existing hash syntax could do this for them, because it is possible to read the URL's hash value from within javascript. All you have to do then is stop it from scrolling when it sees a hash (which is easy enough), and you've got a bit of the URL which is effectively ignored by the browser, but can be read and written to by javascript; perfect for use with Ajax. The fact that Google includes the hash part of a URL in its searches was just a lucky bonus to begin with, but has become quite important since the technique has become more widespread.

I note that people are calling this hash syntax a "shebang" or "hashbang", but technically that's incorrect; it's just a hash that is relevant -- the 'bang' part of the word "hashbang" refers to an exclamation mark ('bang' is a printing industry term for it). Some URLs may indeed add an exclamation mark after the hash, but only the hash is relevant to the browser; the string after it is entirely up to the site's authors; it may include an exclamation mark or not as they choose, but either way the browser won't do anything with it. Feel free to keep calling it a hashbang or shebang if you like, but understand that only the hash is of significance.

The actual term "shebang" or "hashbang" goes back a lot further, and does refer to a #! syntax, but not in the context of a URL.

The original meaning of this term was where these symbols were used at the beginning of a Unix script file, to tell the script processor what programming language the script is written in.

So this is indeed an answer to your question, the way you've worded it, but is probably not what you meant, since it has nothing to do with URLs at all.