[nextlevelwizard]

With any commercial software security matters. You don't want your licensing solution to be craked by editing a file.

Anything that connects to any server or has any sort of networking.

Anything that needs privileges (like installing drivers) needs security.

Anything that reads/interpeds any data given to it needs to have security.

Of course this all depends what you mean by "matter". I can't come up with a program that doesn't need to think about security at all expect something trivial like hello world.