1. If you don't use strict, we won't want to help you.
2. If you still don't use strict, we will NOT help you.
3. It will catch mispelled variable names.
4. It will catch missing '$', '@', '%', and '&'.
5. It will force you to actually know what variables you're using.
6. It will not let you use local unless you specifically say you want to. (Instead, you have to use our to scope globals.)
7. It will prevent variable-clobbering due to scope changes. (You still shouldn't use the same variable name in different scopes, but this helps even if you're silly.)
8. It will help you program better.
9. It elevates Perl from the level of shell-scripting to the level of a true application.
10. It makes maintenance of Perl applications possible. (I'm not exaggerating about this one.)
11. And, the most important reason is "Because I said so."

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.