Popular, I don't know about that.
Did people do it, yes, to all sorts of different parts. Shimano then did it for is and often a bit better, like a hollow cranks, drilled cogs, milled out mechs and grooved or narrowed bar mounts.
Loads of metal in them there cranks. Still probably stronger than most CNC stuff back then.
That's a really neat and tidy job there, most would just be hit and hope and random drilling.
IT picked up a nick name as Drillium (though not sure how and when, think that predates this era 70/80s?) I only really heard it after the early 90s era.
Other things one weenie might do is stip a Flite of it's padding and leather, look under it and you'll see squares. That's a ideal target to get regular drilling...
It's now eaven lighter and bendier to get the comfort back. Oddly more comfortable than you might think with padded pants.
Water could be a problem and mud, but hey they miss whole parts of saddles out now.
Then they brought the carbon version out, I'm not sure if anyone drilled that.