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When Baldur's Gate 3 came out, Steam's overall bandwidth consumption went from around 18 Tbps to 146 Tbps
(reddthat.com)
From Steam's self-published stats.
Baldur's Gate 3 could not be preloaded and weighed in at 125 gigabytes on disk, so when the game left Early Access at 11am US Eastern yesterday, Steam's bandwidth utilization shot up 8x over a span of 30 minutes. I know personally, I saw my download hit over 600 Mbps across a 1 Gbps fiber connection.
Kudos to the system engineers at Valve. It is mind-boggling that they have built infrastructure that robust.
Yeah most games on Steam run just fine without Steam. You can shortcut the exe if you want to.
You can also install it to any drive/USB you want to and use it from there for years, with or without Steam.
GoG is great, don't get me wrong. But the things OP is celebrating it for have been doable on Steam for a very long time now.