The sketchfab publisher exports your model to sketchfab, an online platform to display 3d-models in a webgl environment.
Models are exported as an obj-file and sent over http to sketchfab. This all happens multithreaded, so you can keep working while your models upload. You first need to make an account on sketchfab and get the api-token to be able to upload. The token comes standard with any account.