If you're going to do Ghost and Underworld stuff, it's a Must Have.
It has a general topography of the Underworld in it (in so much as what amounts to maze collection of tunnels, caves, crypts, can have it such a thing), more information on what and how ghost 'live' out their deaths, and a whole lot more, including how to GET to the underworld if you're something other then a Geist or Mage. Also, it's one of the few books that literally goes, "Mages think they know shit, but they don't know dick." Which, as a player of humble mages, is always something nice to hear.
Nope. The only beings in all of WoD who can fuck with time are Mages (who can only do so to their own personal timeline until they become an archmaster), the Gentry (who can, theoretically, live in places of Arcadia who's causality run backwards, because fuck you it's Arcadia), maybe Time Spirits (and that's a BIG maybe), and the God Machine (because fuck you, it's the God Machine). However, theoretically it's possible to do Time Travel stuff in a WoD game. In fact, one of the examples I used for my recent Hunter Quest to describe TFV is Project Backstep, which was the name of a government run Time Travel program in the old late 90s / early 2000s TV show Seven Days (the titular catch being that they could only travel back in time seven days to prevent whatever they wanted to prevent).