(Short) length of technical documentation is a must if that documentation is printed to accompany a product sold to an end user. You cannot sell a pocked digital camera with a five volume textbook on how to handle it. But I'm sure you have also experienced situations where the documentation was brief to the point of becoming confusing.
If the documentation is purely digital, there is no reason at all to limit "length". The only consideration is usefulness.
Unlike Michael B I don't think that volume decreases "findability". That solely depends on proper indexing and an "intelligent" search algorithm – both digital and in print.
Using the example of the pocket camera, there really is no reason not to go beyond the mere technical explanations and include some basic information on how shutter and sharpness of an image relate to each other, or what the numbers on the shutter mean. I always forget those things, and having them handy with the manual of my camera would be a nice feature. This will bloat the documentation, but make it more useful for the target audience of amateur photographers.
(Good) illustrations, detailed examples and other non-basic information also helps understanding, while it drastically increases the size of the documentation. But in a digital (hypertext) manual you can easily "switch" those features on or off with a simple button, essentially creating a short-and-long document in one document.
Of course you might want to print out your documentation for the purpose of backing it up or getting an overview, but that is one special use that should not dictate what the end user gets. Only if the end user gets a printed copy should length be a factor. Otherwise, as I said, the only relevant question is wether the information is useful or not. If it is useful, put it in.