but... why? how does your site or personal marketing/messaging benefit from a random (and quite ubiquitous) emoji as a favicon?

The entire point of a favicon is for quick recognition in the tabs of your browser. How does a rocket ship represent you and your work? How does it help you stand out from all the other designers (and more importantly, tabs of a browser since we're discussing favicons specifically) ? I think you're missing out on some personal branding opportunities.

Also, rationalizing design decisions on the fact that "well, it looks kinda cool" is not going to win over potential clients/ employers.