I took photography in high school when we had Pentax K-1000 manual film SLRs. The ISO was fixed at whatever film you put in, usually 100 or 400. Then you had to set your aperture and shutter speed for the correct exposure. There was a needle (essentially a volt-meter hooked to a photo-diode) in the viewfinder that indicated when the exposure was correct for the film ISO. Typically you would choose a speed or aperture for the scene you wanted, and adjust the other to get the exposure needle correct. To be honest, it was annoying and fiddly, because if you chose the speed wrong, you'd have to take your eyes off the viewfinder to set the dial. But it was really good for understanding how the 3 settings were related.
What I found much more convenient were cameras that had the half-auto aperture-priority mode where you manually set the aperture, and the camera sets the speed. As explained in the video, having aperture-priority means you are actively choosing the depth-of-field and you can change it for each shot if you want. You can increase the depth of field to make everything sharp, or you can reduce the depth of field to put bokeh in the foreground or background. For example, if I'm in the mountains and see pretty flowers in the foreground, I can quickly take 3 shots, one with the mountains in focus, one with the flowers in focus, and one with both--to see which is the best.
Shutter-priority is similar, where the shutter speed you choose determines the motion blur. For example, if you're shooting your kid on a bike, you can choose a high speed to make everything frozen, or you could choose a low speed and follow the subject to give a background motion blur--and you can take both shots within a second of each other.
As the other commenters say, this is what has carried over into DSLRs and can be really useful. Once you learn the trade-offs and choose A or S mode, you have a lot of control over the image. The inner ring of the lens usually controls the aperture in aperture-priority mode, so you have exposure control on your left hand holding the barrel of the lens. And with auto-ISO, the camera will increase the ISO so you can still shoot at 1/60 indoors to avoid motion blur. You never have to take your eyes off the viewfinder while adjusting the exposure and you have a lot of control over the outcome of the photo. With practice, the hand motions become automatic, and you can make split-second changes to capture a beautiful shot of that fleeting moment.