Developing by inspection made sense during the period 1880s-1950 when most amateur films were orthochromatic and you get by with see-sawing the film in a tray of developer, then stop bath (I was too poor to buy this and used water) and then fixer. Washing could then be done in a sink or a pot with film clips attached to the film ends.
To do all this even reasonably effectively, you had to see what you were doing so you could stop the first tray process when the film looked 'thick' enough. I had a Kodak safelight with four or five different filters, one was green for panchromatic film and another was red for ortho. The green sure was dim and I never did any ortho, so the red was wasted. The safelight also came with two enlarging filters (fixed grade and VC) and another filter which I never used and have quite forgotten what it was for. Maybe a clear for reading the Kodak Darkroom Dataguide which we all owned way back then...
I did this a few times but was never entirely satisfied with the results. My Verichrome Pan 616 films hand-processed with the aid of that green filter showed an annoying level of fog which I I then contact printed, but as I didn't own an enlarger big enough to handle that film I never put those negatives (which I still have, somewhere in 50+ cartons stored in our garage) to the blow-up test, and likely now I never will.
Ultimately it was so much easier to use an old Paterson Universal tank someone had given me, to do my films.
As I believe someone has said or hinted at elsewhere in this thread, this was/is an obsolete technique used mostly by amateurs of that era with little or no regard to quality results. This I reckon sums it up.