As a site admin, I don't want my first time users to have to watch spaces when they are doing on boarding on Confluence. Let them make this decision later. Please add a skip option in there too.
The default onboarding experience can be turned off by system administrators by going to Settings > Manage apps
And then changing the filter to "System" and searching for "Confluence Onboarding" there should be 1 matching add-on. Click on it and then click on the "Disable" button.
This will disable the onboarding experience and users will instead be taken straight to the dashboard on their first login without being required to watch or create a space.
In Confluence 6.14.0 (to be released late January 2019), we replaced the existing onboarding flow for normal users (i.e. non-admins) with a simple modal dialog when they first login to Confluence. Users are no longer asked to watch a space.
Upgrading to Confluence 6.14.0 or newer will resolve this issue.