Wordpress if/while or while loop

When including the standard wordpress loop, when do I need to use the 'if have posts, while have posts, the post' or the 'while have posts, the post' ?

Do I always need to use the if/while, or is it just on some pages that I need to use just the while loop ?

I feel that I have included the if/while on all pages and if that is the appropriate way...

Can someone enlighten me?