SharePoint developers - we do like GUIDs, don’t we. We all read RFC4122 both once and twice. And now with SharePoint Framework and the goal to embrace all them Macintosh and open source people - they gotta have their fair share of GUIDs. And to aid with that the SharePoint Framework got some really nice GUID features, although a bit unpolished as you might notice - but this is all preview bits at the time of writing.
Do you write code that potentially can throw an error or an exception? Oh, you don’t - but sure you use a web service or external service or something that can throw an error. Well, it is you responsibility to handle the error and make sure to inform the user in a good way that something bad happened. With that I mean, do not show just a Guid. With the SharePoint Framework being all client side I think it is important to have control of your client side Web Parts and make sure that you properly handle and display error messages in a consistent way.
SharePoint Framework is all about rendering stuff on the client side, avoiding the long overdue ASP.NET Web Forms technology that SharePoint (Online) is still fundamentally based on. When rendering things client side everything is done asynchronously, to avoid locking down the UI threads and having a user experience that is fluent. In order to give the user good feedback that things are happening in the background, you need to have some kind of visual cue that tells the user - hey I’m doing stuff now, gimme a minute.