From an early-music perspective, this is all driven by simple rules. There were 3-, then 4-, and now 5-line staves. Vellum and parchment were expensive, so the aim was to make the notation as compact as possible. As music evolved over time, individual voice parts spanned wider ranges and the staves needed more lines. (6-line staves may be significantly harder to read; don't know.) Materials (paper!) eventually became cheaper and affordable. The need to conserve materials also led to early music being written in separate parts rather than scores, so simpler parts didn't waste empty horizontal space lining notes up with more florid parts.
The clef symbols identified "middle" C, the F below, and the G above. I've seen multiple forms for the F and G; modern notation has one surviving form for each. They could be on any line of the staff, to suit the range of the part. (I've even seen clefs on spaces.) They can have octave shifts, usually indicated with a little 8/16/32 above or below the clef. (You might see a little 8 below the G (treble) clef of a modern tenor vocal part, but commonly now that is simply assumed and omitted.) Ledger lines were never used. (You'd have the space the staves farther apart, and you'd get less music on the page.) If the part ranged far enough, you'd have to use a new clef to keep the part on the staff. Generally you tried to do any clef shifting at the beginning of a staff. A custos ("direct") at the end of the preceding line served as a clue to what was coming.
As to ease of reading -- music notation is a language, and like any other language you (a) learn the rules and (b) practice applying them. We all learned the sounds of the letters of English (substitute your own native language here), then learned to combine sounds into syllables and words. With practice, we became fluent readers. Musically, I started out on the piano, and I became 'fluent' with treble and bass clefs. I simply recognize the meaning of notes on every line or space, and nearby ledger lines. If we commonly had floating clefs, instead of learning these fixed relationships, we would all learn to apply the relative-to-the-clef rule all the time -- it would simply be a part of the language we use. At one point I was teaching myself to read C-clef on the middle line. At first I was doing the relative translation for every note; then I was recognizing more and more notes by fixed positions, learning a 3rd clef. Learning to parse floating clefs on the fly would be much more powerful/flexible, but I simply don't encounter it in the music I see, so I don't get any practice at it. (But consider that we have time signatures and key signatures, and these affect the way we interpret each measure. They can change throughout the piece, and we apply these rules on the fly. We learn to do whatever is commonly required.) Writing music with these archaic rules will restrict the comprehensibility to a smaller audience, much as writing English with obscure vocabulary or foreign words would.
(no subject)
The clef symbols identified "middle" C, the F below, and the G above. I've seen multiple forms for the F and G; modern notation has one surviving form for each. They could be on any line of the staff, to suit the range of the part. (I've even seen clefs on spaces.) They can have octave shifts, usually indicated with a little 8/16/32 above or below the clef. (You might see a little 8 below the G (treble) clef of a modern tenor vocal part, but commonly now that is simply assumed and omitted.) Ledger lines were never used. (You'd have the space the staves farther apart, and you'd get less music on the page.) If the part ranged far enough, you'd have to use a new clef to keep the part on the staff. Generally you tried to do any clef shifting at the beginning of a staff. A custos ("direct") at the end of the preceding line served as a clue to what was coming.
As to ease of reading -- music notation is a language, and like any other language you (a) learn the rules and (b) practice applying them. We all learned the sounds of the letters of English (substitute your own native language here), then learned to combine sounds into syllables and words. With practice, we became fluent readers. Musically, I started out on the piano, and I became 'fluent' with treble and bass clefs. I simply recognize the meaning of notes on every line or space, and nearby ledger lines. If we commonly had floating clefs, instead of learning these fixed relationships, we would all learn to apply the relative-to-the-clef rule all the time -- it would simply be a part of the language we use. At one point I was teaching myself to read C-clef on the middle line. At first I was doing the relative translation for every note; then I was recognizing more and more notes by fixed positions, learning a 3rd clef. Learning to parse floating clefs on the fly would be much more powerful/flexible, but I simply don't encounter it in the music I see, so I don't get any practice at it. (But consider that we have time signatures and key signatures, and these affect the way we interpret each measure. They can change throughout the piece, and we apply these rules on the fly. We learn to do whatever is commonly required.) Writing music with these archaic rules will restrict the comprehensibility to a smaller audience, much as writing English with obscure vocabulary or foreign words would.