Why auto-boxing marked as a warning?

If you don't expect performance issues (in terms of micro-optimization) you can safely disable this warning. It is just an indication in case you're not aware that auto-boxing happends here. In business-logic code where you have I/O overhead (due to DB transactions or disc access) auto-boxing hardly becomes a performance issue.

Autoboxing can contribute to the developer creating a bug related to the "remove" method of Collections, though this is probably a pretty obscure bug.

I've encountered this bug when I used a random number generator to select the index of an item to remove from an ArrayList. The generator returned a long primitive, which I accidentally tried to use as the parameter for List.remove(int index). The compiler converted the long to a Long and used it in List.remove(Object o), which gave totally different behavior. Luckily, an assert statement caught the error quickly.

According to this discussion of this issue with "remove", someone else ran into a similar problem where their int unexpectedly acted like an Integer, though I don't understand how that happened. Why aren't Java Collections remove methods generic? (see comment by ScArcher2)

I was going to disable this Eclipse warning but the following article made me consider not to. I'm still not completely sure but it looks to me like those might be good reasons to just avoid autoboxing.

https://effective-java.com/2010/05/the-advantages-and-traps-of-autoboxing/