Absolutley. Although in some cases, you can read them, try to make sense of them, and use them to make the website behave in a manner you can't otherwise.

This isn't a real example, but sometimes you'll see something like this:
http://www.flyertalk.com/forum/trave...ostsperpage=50

For example, on a forum where you can select the number of posts per page that are displayed. The maximum is usually 50 to 100 but some discussions span hundreds of posts. Sometimes you can get away to messing with that number to get a big, long discussion that spans many pages to show up in one - by changing that number to 9999 or something.

And you can mess with them in other ways to manipulate the way pages behave, depending on what the developer is using those values for, and if they've done any checking server-side to see if anybody has entered unexpected values.