Specifically in the context of Baroque trio sonatas. If part books are preferred, then what is the point of printing such works in score in the first place?
When you are practising on your own, separate from the other members, then an individual part book is more convenient. You have less music to look at and follow, fewer page turns to make.
When you are playing together, having to co-ordinate what you play with the other members of the group then a full score is essential so that you can follow what the other members are playing in places where you have a rest marked and so that you know exactly when to come in when your part starts again.
A huge amount of scanned, period music at imslp.org is parts only.
That's frustrating to me when I just want to study the compositions, not perform them.
I've assumed the absence of an ensemble score is because:
- the music was printed primarily for performance where each player only needs their part, and
- printing was much more expensive then so they wouldn't have added the expense of the extra printing. From the typesetters perspective, they have to do double the work!
With modern software and printers, it's easy and cheap to print full score and parts.
I don't know what chamber musicians prefer but regarding why print a score?, it seems one important reason is study and analysis.
I happen to disagree with some of the acccepted answer. It only takes a couple rehearsals to know enough about what the others are doing in your rests that single parts work just fine. You want a reference score available to coordinate questions and check for misprints. The advantage of single parts is that you have far fewer page turns to deal with.
That said, some quartets are transitioning to tablets rather than paper music. Once you do that, page turns don't matter much (just a foot-tap), so the use of a single part vs. full score is entirely up to each player's discretion. As a side feature, it's really easy to add and remove markings!