So in general there are two opinions on absolute versus relative URLs:
- use relative URLs because easier to move around
- use absolute URLs because easier to move around
Confusing, yes. The argument boils down to that migrating things with relative URLs you don’t need to change domain. The counter argument is that you might need to change levels or URLs and then relative suddenly turns into complete nightmare.
Regardless of which camp is “right” — WordPress is firmly in the absolute URL camp. All it’s API functions will output absolute URLs and it’s intended workflow for anything related in it.