It used to be common and useful. I did this even after Valve shipped a native Linux TF2 as at the beginning the Wine method gave better results on my hardware. But that time has long passed as Valve has integrated Wine (Proton) and in almost all cases the Linux native builds will outperform Wine (and Steam will let you use the Windows version via Proton if you want even if there is a native Linux build).
So while I suspect that there are still a few people doing this out of momentum, habit or reading old tutorials I am not aware of any good reasons to do this anymore.
Launching Steam games outside of Steam can be very difficult. Some games outright won’t allow it.
Steam provides native libraries such as the overlay, networking and matchmaking tools, achievements… You need to have Windows versions of these which wouldn’t be distributed by default in the Linux version of Steam.
In the past Steam just didn’t run under Linux, so you had no other option.
It used to be common and useful. I did this even after Valve shipped a native Linux TF2 as at the beginning the Wine method gave better results on my hardware. But that time has long passed as Valve has integrated Wine (Proton) and in almost all cases the Linux native builds will outperform Wine (and Steam will let you use the Windows version via Proton if you want even if there is a native Linux build).
So while I suspect that there are still a few people doing this out of momentum, habit or reading old tutorials I am not aware of any good reasons to do this anymore.
But why would you run steam under wine? The games themselves make sense, but steam not so much.
There used to be a time when Steam for Linux didn’t exist.