What does sanitizedError mean, and how to use it?

HI,
Can anyone help to explain the following chappter from meteor doc? what do “mapped to a sanitized version on the wire” and “sanitizedError field” mean?

I understand how to create an Meteor.Error and have it returned to the client, but I just want to understand this part so that I can be sure there won’t be any traps.

Thanks for your help!

http://docs.meteor.com/api/methods.html#Meteor-Error

If a method function throws a different exception, then it will be mapped to a sanitized version on the wire. Specifically, if the sanitizedError field on the thrown error is set to a Meteor.Error, then that error will be sent to the client. Otherwise, if no sanitized version is available, the client gets Meteor.Error(500, ‘Internal server error’).

And, if you throw it at the server in the end of a promise chain, in a …catch, why does the server crash?..

I’d like to understand this doc extract too !