What's the name for when you write multiple voices on same staff? And are there any cons?

Question

When I transcribe music for piano I always use the grand staff and notate the left hand (which often is the bass voice) on the lower staff, everything else on the upper one. When I do it for a guitar I find that one staff sometimes is enough.

What is the English name for these two methods? In Italian the first one is called "a parti late" and the second "a parti strette" which literally means with wide/narrow parts.

Most of the times on guitar (classical fingerpicking) you don't pick more than 5 notes at the same time and you only pick one bass note at a time that can't be lower than E (3 ledger lines is not that hard to read) so one staff seems enough for me. What are some pros of using the grand staff instead of this method when writing for guitar?

Answer 1

In English, it's called closed score. Open score means one instrument or voice per staff, as with most SATB choral music.

Open score is easier to analyze, but often harder to sight-read because the shape of the fingering hand (guitar) or each hand (piano) isn't immediately visible on the page. Open score also occupies more space on the page, so it requires more page turns.

Piano music might have half a dozen independent voices on the grand staff (Bach fugues), or spread over three or even four staves (Liszt).

Answer 2

No advantages for guitarists. They are used to reading everything on the treble clef, even though they play an octave lower than written. If they had to read bass clef as well, te notes would only go as low as the third space up, so there's no advantage.