Which custom error pages are important, beyond the customary 404?

[fjpoblam]

I know it is customary to have a custom 404 (Not found) page on each website. This I already do. As Microsoft recommended, each is at a minimum 512K in size. And I regularly check error logs for all sites to watch for them and react accordingly.

 

Question is, how much effort should I devote to maintaining *other* custom error pages? These I currently do for each and every site, though error logs never show them happening: 400, 401, 403, and 500.

 

Is it likely safe to drop them and eliminate the effort of maintaining them? (Has a "best practices" article already been written, somewhere, which I may read on this topic?)