Here are some reasons why I bought the camel book, even though the man pages are fine:

• It's a good book. It's more entertaining than the man pages and packed full of historical anecdotes and such.
• It's nice to give a little money to Larry and the other writers, as well as O'Reilly, which does a lot for the Perl community.
• The number of copies of the camel that O'Reilly sells are often cited as evidence of how many Perl programmers are out there.