The main reason for writing a unison like this has little to do with fingering and everything to do with the music's structure. Unisons in keyboard music quite obviously use the same key, so their point is to show how the voice leading works. In the example above, they show that two lines in contrary motion meet at the tonic.
As I've mentioned in my comments, a rest could be substituted for one of the notes in a unison, but your understanding of that line's phrasing would change, and hence your presentation of the phrasing might very well change as well (for example, by shortening the last note before the rest so that it doesn't give the impression of meeting the other line in a unison).
It is no means unusual that one of the notes in a unison may have a shorter note value than the other. This may be dictated by motivic or thematic requirements. I'll give an example from J. J. Froberger's Ricercar I (FbWV 401).
In this excerpt, the first bar-and-a-half conclude the previous section, and a new one starts at the end of m.87 with a statement of the ricercar's subject (in blue) matched with a short second subject/motif (in green). Momentary unisons are marked red. The first one is a bit unusual in that the entries of the unison are staggered. You would normally play this unison as a crochet before the bar line, followed by a dotted minim after the bar line. (On an organ, it would be hypothetically possible to play both voices separately on different manuals, although I doubt a performer would - the inner voices shift between hands, and there isn't really any tidy spot to bring both hands back together on the same manual.)
The second unison is pretty straightforward: you would hold the F for the complete measure.
But you should be able to see why Froberger wrote it this way: the individual voices make sense as written, and you want to try to give an impression of those lines as written, even though you will need to fake it a bit.
Here's the complete ricercar (unfortunately in a MIDI rendition). It is a really lovely piece of music, IMHO.