Q: Do I need BRIDGE/BOOST?
A: Only if (a) you cannot run an Ethernet wire from your router to any Sonos component in your home and (b) connecting via WiFi isn’t good enough.
Q: When is WiFi not good enough?
A: For everything beyond simple music streaming. If you want to run PLAYBAR with SUB and two PLAY:1 or PLAY:3 for instance.
Q: I have BRIDGE. Do I want to upgrade to BOOST?
A: If everything is working OK, no. If you have dropouts due to bad wireless coverage, yes as Sonos Boost have 50% better coverage than Sonos Bridge
Q: I’m about to buy a Sonos system. Which one should I choose? Bridge or Boost?
A: It doesn’t matter. Sonos Bridge have now been discontinued :p