I wouldn’t say obsolete, but it’s not required at this point, given all of the advancements in router’s capabilities over the last 10 years or so.

I continue to use mine for those speakers that can connect to it, while those that don’t connect directly to my Wi-Fi signal. 

Do you suggest that I keep Boost plugged in? If I’m understanding correctly, if I keep Boost plugged in, it will  work with my older speakers but not hurt the performance of the ERA 300’s which will automatically connect to my mesh wi-fi system?

I keep my Boost connected for my speakers that can use it. The portables and Eras just connect to wifi themselves and aren’t affected by the Boost. I continue to use the Boost as my router isn’t the best! Makes the set up more stable. 

I’d tend to agree with @SarahN , although I have no evidence to support ‘more stable’. I do prefer to keep the majority of my music traffic off of my WiFi’s network…but that’s more likely habit than any evidence one is better than the other, at this point. 

It could be @Airgetlam that I’m just guessing my setup is more stable using SonosNet but before I got the Boost, I certainly had more dropouts I seem to remember. I work on the premise of ‘if it ain’t broke, don’t try to fix it’ 

I think if I could be bothered to look into getting a better router than my crummy BT one, then maybe I could ditch the Boost, but it helps a lot with all the Sonos gear I do have.

Plus I got my Boost last year, second hand for just £45 off eBay so it was good value really

Try it. Ensure that the WiFi credentials are entered into the system first obviously. 

https://support.sonos.com/article/switch-sonos-between-a-wireless-and-wired-setup

My Sonos system’s performed distinctly better since I moved it all to a 5GHz WiFi mesh (except for the home theatre master players which must use 2.4GHz WiFi).