Being able to start in gear was a common practice in the day. It wasn’t until the Feds decided that we the people were too stupid to start a vehicle without taking out the garage door or worse that the safety measures like clutch to the floor etc. tomfoolery became the norm. The advantage of being able to start with the Transmission in gear is great including starting after stalling out on a steep hill and the like. That act alone may save you from a long roll to the bottom. Also if your clutch actuation goes out you can start from a stop in gear then actually shift up through the gears without a clutch using the momentum point with no gear grinding (mostly). I had to do that once when the bracket that held the clutch cable to the firewall in my 1972 CJ5 tore off the wall while shifting leaving me with not clutch in the nowhere lands of Montana.
And you can start with a dead battery if you are on a hill. When I was very poor and couldn't afford a new battery, this was how I started my car every time.