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Why is it recommended to split a large document into several parts and include them with \include? Is it only a relic of the past times when computers and LaTeX compilers were slower, or is it still up-to-date? What are the pros and cons of this practice, also in terms of interaction with other external tools (version control, find/replace, et cetera)?

Motivation: I've found a recent discussion that mentions this practice ( Writing and Managing Thesis in LaTeX, Everyday LaTeX and workflow?), as well as a comment that criticizes it in an answer to Everyday LaTeX and workflow?. A couple of months ago, I asked the same question in a comment to Techniques and packages to keep up with good practices, but it's probably better to ask this here again as a "real question".

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You can find your comments under the 'activity' tab on your user page – cmhughes Sep 26 '11 at 19:11
@cmhughes: thanks for the tip! I have now found my old comment and edited the question accordingly. – Federico Poloni Sep 26 '11 at 22:04

For one thing you can significantly speed up compilation time by including only certain files, e.g. when you have tons of graphics.

Another advantage is that you can manage more easily documents on which several people work simultaneously.

And finally it gives added reusability of the given parts (e.g. you want to publish the handouts of your collection of laboratory experiments, but you also want to be able to print one at a time and/or give the description of one experimets to your students).

So I guess it really depends on what you have in mind.

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I thought externalizing was the way to go when you have heavy graphics, so I am not totally convinced by #1. Could you be a bit more specific on #2? Are you assuming the group uses revision control or not? Regarding #3, it seems an uncommon use case to me. In most cases, you want to do small modifications to those files (e.g., changing all "in this book..." to "in this handout..."). – Federico Poloni Sep 26 '11 at 21:55
#1: externalization is certainly an important option. I personally put most of my graphics (I use TikZ) into separate files. Then I can compile a larger document without the graphics much faster. This is the way I do it if the figures are not the part I am currently working on. The method also allows me to reuse the figures. – Count Zero Sep 26 '11 at 23:16
#2: I have never had the opportunity to use LaTeX in that context.:) But consider journals an example. #3: This is an actual use case of mine: I have a lab class material at the university consisting of handouts for each session. Not all are necessary during a term, but we need to have them in one place, printed as a single book. – Count Zero Sep 26 '11 at 23:27
#1 is irrelevant if you have a good editor (emacs has C-c C-r, compile-region). #2 is irrelevant when using a decent VCS. #3 is the only one that might convince me. – mbork Nov 16 '12 at 19:46

Splitting a large document into parts is A Good Thing; with today's front-ends or editors it's quite easy to jump from one part to the other.

The choice between \include and \input is very subjective. \include was born when computers were slow and typesetting a complete book could be a good occasion for having a coffee, maybe two. It has its uses also now, because it can solve cross references even when the chapter is not \included. (See also CountZero's answer for another use.)

Personally I don't mind if some references are not solved during trial typesetting sessions, when I'm more interested in the overall shape than in precise line and page breaks. It's easy to comment out some lines in a well-structured main file, but the same can be said about strings passed to \includeonly; however using \input and commenting doesn't require to duplicate the list of files. Not a big deal, of course, but when the chapters are many, it might be a nuisance; on the other hand, writing and reading from .aux files adds a little overhead.

With a modern computer, the times needed to typeset a chapter or an entire book are not very different, unless the book is very large, or it has many graphics using TikZ or PSTricks that slow down the process. In these cases, using \include can save your time.

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Another example for some time-consuming parts of a document are source code listings processed via the listings package. I personally use \include because I tend to work in small, quick typeset cycles. I also like to be certain that every reference works, these ?? reference make me nervous. Unfortunately, the todo package doesn't list all items in a partially typeset document, but that's not that big of a problem for me. – 0x6d64 Sep 26 '11 at 19:05
You say that it is a good thing, but you do not give reasons why it is so. I am interested in knowing the motivations here; could you argue a bit more? Actually, your last paragraph here seems to support the opposite view --- just keep everything together and avoid the hassle. – Federico Poloni Sep 26 '11 at 21:59
Splitting the source makes easier to have all the files open at once, for example. It also helps when recovering a corrupted file from a backup. – egreg Sep 26 '11 at 22:50
My phd thesis takes about 5 minutes to compile on a modern 4 core PC. The time consumption comes mostly from the figures (about 200 images). So no matter how fast a computer is nowadays, I recommend usage of \include in any case. – Matthias Pospiech Sep 27 '11 at 8:27

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