Meaning: writing one letter or word when you should write two - leter instead of letter, or The, when you meant The The.
Usefulness: 1 (Who knew typos were so specific? Here's to the next level of pedantry.)
Logofascination: 1 (hapolography has nothing to do with mishaps, as I wrongly thought. Haplo means single or simple, whereas in mishap the hap means good luck, fortune, chance, - and, yes, eventually happy - and it's the mis- that indicates that things have gone awry. In case you were wondering, when you write two letters or words instead of one, it's dittography; the the rather than the.)
In the wild: while it could be used quite often of English, I have only seen it in scriptural contexts, where the exact meaning of the Greek or the Hebrew (tricky languages to write) can be quite important.
Connections: haplography - cosmography
Which is used in: G&P, Second Book, VIII: How Pantagruel, being at Paris, received letters from his father Gargantua, and the copy of them. Gargantua had many sensible things to say, not the least of which was:
Let there be no history which thou shalt not have ready in thy memory; unto the prosecuting of which design, books of cosmography will be very conducible and help thee much. Of the liberal arts of geometry, arithmetic, and music, I gave thee some taste when thou wert yet little, and not above five or six years old. Proceed further in them, and learn the remainder if thou canst. As for astronomy, study all the rules thereof. Let pass, nevertheless, the divining and judicial astrology, and the art of Lullius, as being nothing else but plain abuses and vanities.Wiktionary defines cosmography as the creation of maps of the universe, and Cotgrave as 'the description of the whole world'; tasks more Sisyphean than mine, and closer to physics, I think, than geography.