Tweaking past versions are useful for general and local manipulations. It is nice to go back at a later date and take a sequence of manipulations apply them to other source files and then slightly tweak the history.
Right. Practically, I usually create several versions anyway and compare the result afterwards. How do they show the history, in a tree?
I don't think it is incorrect. I have not been able to save multiple verions of the same source file without exporting or copying the source file. For example if I have one raw source file and I want to save a b&w version, a full color version, a sepia version, a cropped version, and a vignette, I need to either export each version or make copies of the original source and apply different operations to each copy.
You create versions by pressing option + G (version from Master) or option + V (creates a duplicate version from the one you have selected). Both definitely do not increase the size of your library (substantially, they are small text files). To do what you want, you can create a version which is in full color, sepia, cropped, b&w, etc. and they will not take much more space than the original file (could be RAW, jpg or any other format Aperture can read). It does not require exporting.
Practically, I don't use option + G all that often, I almost exclusively use option + V (duplicate version, i. e. you create a duplicate based that includes all previous edits that have been made to the master file): I would make some tweaks to an image and then `branch off' some edits, e. g. making a sepia version and compare it to a b&w version. Practically, I would make several (sometimes temporary) versions with different sepia intensities and choose the one I like best. Then I can cycle quickly back and forth to choose between them.
It sounds to me that you haven't used Aperture correctly (no offense, it's a complicated software package), you don't (rather: shouldn't) export anything -- unless you want to/need to use an external editor.
The concept of versions has been part of since Aperture 1.0.
Lightroom on the other hand, allows me to have multiple saves at different points in the history and saves the entire history for each version of the same source file and doesn't require exporting.
With the exception of having to make `manual waypoints' in history, Aperture can do that, too. Having the history sounds handy, though, but I wouldn't know how to implement this nicely (in a tree perhaps?) without bloating the whole UI.