what do you use ragged-bottom for?

[Keith E OHara]

I'm fixing a bug involving the ragged-bottom setting (issue 3281).  By default, 
ragged-last-bottom=##t so the last page can have blank space at the bottom.  Currently, 
"ragged-bottom" is implemented to *always* under-fill the page, *never* 
compressing to fit one more system.

As a default, that is wrong, because all the other pages are best-fit, while 
the last page is under-filled.  The situation has caused me quite a lot of 
confusion: wondering why LilyPond likes to put the last system on its own page, 
decreasing the staff-size, or trying page-turn-breaking -- and then wondering 
why so much material moved back to earlier pages, so that the last page is 
again the least full.

For now, as a workaround, in these cases we can say \paper { 
last-ragged-bottom=##f }, which can go selectively in individual \bookpart s if 
need be.

So 'ragged-last-bottom' should allow a gap at the bottom of the last page, but 
let the page fill as the others are filled.  But I do not know what 
'ragged-bottom' should do.  This is the option that applies to all pages.  
Werner sees some sense in 'ragged-bottom' meaning that pages are neither 
stretched nor compressed vertically, but cannot think of an example where this 
behavior is useful.  (I wrote code with a new option to let us switch the 
behavior, but have no idea if the added complexity gives any benefit, or how to 
best set the defaults.)

So for what kind of music do you use ragged-bottom=##t ?

The manual (currently) suggests it for scores, where maybe just two systems fit 
on a page; but then the systems are closer than they need to be on the looser 
pages.  To give adaptable space at the bottom of the page, it is better to use 
\paper{ last-bottom-spacing #'stretchability = 120 }

Sometimes we do want fixed vertical spacing of the music on the page; we can 
make the 'minimum-distance as big as 'basic-distance, in all the spacing 
settings, but that user-interface is difficult.

Maybe ragged-bottom=##t should continue to always under-fill pages, as it does 
now?