When working with existing sites or content management systems, you have little say on where and when jQuery is loaded. To complicate matters, some pages may have jQuery auto-loaded, and others may not (yay for performance boosts, nay for client-side plugins). Do you bite the bullet and write unmanageable scripts? Or do you believe in RequireJS and dodge the bullet matrix-style?
Ever wanted to send request headers from jQuery instead of the “code-behind”? You can easily tweak the ajaxSetup object to do this.