User ID in the sharing link is useful in at least one situation.
There are some badges:
- Announcer
Share a link to a question later visited by 25 unique IP addresses. This badge can be awarded multiple times.
- Booster
Share a link to a question later visited by 300 unique IP addresses. This badge can be awarded multiple times.
- Publicist
Share a link to a question later visited by 1000 unique IP addresses. This badge can be awarded multiple times.
Your user ID in the link keeps track of the number of visits following the link you shared even if you post the link outside Stack Exchange network (in social media, personal website etc.).
To answer the second part of your question, viz.
Are there any circumstances where I should remove it before posting the link?
I reckon it's completely up to you. You might not want to associate your Ask Ubuntu username with your online persona in other places. In that case I think it's wise to remove the unique user ID before posting the link.