It led to a long conversation because it is a useful technique, specially for DIYers.
Commercial manufacturers prefer cold rolled steel sheets, around 1mm thick (#18) because it is strong, cheap, versatile, it can be spot/resistance soldered to build up complex shapes, etc.
But it needs heavy expensive machinery such as mechanical presses, forget getting those at home.
Also custom made dies for different shaped holes.
Any kind of round holes, rectangular for toggle switches, IEC connectors, slots for slider pots, the works.
Inexpensive per finished unit but machinery setup means minimum production of anything is 50-100 units 😲
Steel also requires surface finishing to avoid instant rusting (oiling surface is fine in machinery but not in home Audio equipment) and platers charge for a "minimum batch size", say 50 kg.
So custom making chassis is out of the question for DIYers.
On the contrary, Aluminum is your friend: softer, relatively easy to work with, you can use hand tools or a home/desktop CNC machine, it does not need surface finishing except for cosmetic reasons, VERY DIY friendly.
But it has its own quirks, one of them being cutting tool galling.
Most of the thread has helped to deal with that 😄