In the 1970s I worked at a number of retail camera stores. They all used off-site labs.
I also worked as a professional photographer, and had colour work developed and printed by a professional lab. Except when I was myself working in such a lab, when I did my own colour printing.
I also did my own black and white developing and printing.
Somehow I also found time to finish one university degree and start another
.
During that time, film and photography was booming. Many people used slide and/or movie film, but even more took colour pictures on colour print film. Colour print photography became even more active at the end of that decade when one hour processing became prevalent.
The results I received from the pro lab were great, but I also saw lots of good results from the amateur labs - lots of happy customers.
There wasn't much black and white going through the amateur labs though. Most people were either shooting colour, or doing their own black and white. There were a couple of professional black and white labs in town, but I didn't use them.
I knew people who were doing colour at home, but didn't do that myself, as I always was either working in a lab or had a lab available.