1. If the appendix was both useless and deadly (before procreation), there would be a strong evolutionary pressure against it, so it likely is unobviously useful

2. Western diet possibly causes problems with the appendix - "Appendicitis is uncommon in rural Africa and Asia"

3. Anatomy involved with immune function or microbiome is hard to understand function.

From links:

The peak incidence occurs in the 15- to 24-year-old age group. However older individuals are more likely to have complications and die from the malady. Symptoms of appendicitis in older people frequently are not as clear-cut as are symptoms in younger people.

People with acute appendicitis often think they would feel better if they just could move their bowels. To encourage a bowel movement, they take a laxative. This is a serious mistake, one that may lead to rupture of the appendix.

https://www.sun-sentinel.com/news/fl-xpm-1987-04-14-87012404...

https://www.scientificamerican.com/article/what-is-the-funct...

Also interesting is the idea that the appendix is a local optimisation. If a smaller appendix was more likely to get appendicitis, it might remain a vestigial organ rather disappearing completely, even it the organ has no function, because there is an evolutionary advantage to having the current rather than the smaller size

Very smart!

One of my favourite pastimes with Hacker News is thinking about how commenters have been trained by playing games to follow incentives and game optimisation (gaming the system).

Slightly off topic, the surgeon who had to remove his own appendix.

https://www.bbc.com/news/magazine-32481442

There are a couple more up to date theories on its current utility