> However, when it comes to 2.5G, I struggle to find one good reason to use it; such a tiny step-up in bandwidth, and for what?

Portability and heat. You can get a small USB 2.5G adapter that produces negligible heat, but a Thunderbolt 10G adapter is large and produces a substantial amount of heat.

I use 10G at home, but the adapter I throw into my laptop bag is a tiny 2.5G adapter.

I’m sure it depends on the model, but in my experience if you force a 10G copper transceiver to 2.5G the insane heat generation goes away. I don’t have any Thunderbolt 10G adapters, but I’m kind of surprised they’re much larger. A SFP+ transceiver is the same size as a SFP one.