This is in regard to routing and rendering. Client side routing pretty much dooms Wayback machine support - Google should still be able to index it because it executes javascript, but not all archiving services do.
Client Side routing is good for Offline Support and may be a little smoother.
Server side routing can provide much better support for javascript-disabled devices. Offline can still be supported by emulating the routing in the service worker.
Anyway the basic question is in the title: very important? not important? Thoughts?