Here's my setup:
My Internet at home comes from a 4G modem, because that's the best deal in my area in terms of price/speed. However, my speed is reduced to 3 Mbps after using 150 GB per month, but that's usually fine as I usually stay below 150. It does happen that I have to endure slow speeds for a few days during the last days of the month, though.
I use a Google Nest Wifi with one router connected by Ethernet to the 4g modem, and one more Google wifi (also acts as speaker) to enhance the signal.
I also have 6 Google speakers in various rooms throughout the apartment (3 Nest Audios, 1 Home Max, 1 Home Mini, and 1 original Home.)
I have made those 7 speakers into one group, and quite often I use Spotify to play on the entire group so they music plays in sync in the entire apartment.
Now, my question is: Will this consume more Internet data than simply casting to one speaker? For example, let's say I stream an album that would usually require 100 MB of data. I would assume that when this plays on all 7 speakers, this is only transferred once from the Internet, then transmitted on my local network to all the speakers.
Is that true though? After all, most people's data plans on home WiFi are unlimited, so it's not entirely unthinkable to me that Home was designed so that each speaker streams the music from the Internet. I see in the Google WiFi app that all speakers seem to have consumed considerable amounts of data during a month, so this makes me wonder.
So while I assume the former, I would like to ask whether someone understands the inner workings of the Home/Nest system well enough to give me a concrete answer here.