Why serve 1x1 pixel GIF (web bugs) data at all?

Question

Many analytic and tracking tools are requesting 1x1 GIF image (web bug, invisible for the user) for cross-domain event storing/processing.

Why to serve this GIF i

Answer 1

Some browsers may display an error icon if the resource could not load. It makes debugging/monitoring the service also a little bit more complicated, you have to make sure that your monitoring tools treat the error as a good result.

OTOH you don't gain anything. The error message returned by the server/framework is typically bigger then the 1x1 image. This means you increase your network traffic for basically nothing.