Just to add to why you would or would not want to use the passphrase vs. the abbreviation - I've personally found that I find it much easier to actually type a password that consists of words, names or "nonsense words" generated by Markov chains (though not usually ones generated by letter frequencies).

I am often comfortable entering in a given password on a device on which I am not comfortable unlocking my password database (or entering my password database password + keyfile), but I usually have a device which does have my password database on it (phone, laptop, etc), so my application is "it doesn't have to be memorable, it just has to be something I'll enter without making a typo". For whatever reason, I find that entering in "tidlotexidaifol" would be harder for me to do accurately than "tidy lot existence daily following" or "tidylotexistencedailyfollowing".

That said, I like this approach, because some sites (like Bank of America, shockingly), restrict total password length, making a "very long password with relatively low entropy per character" approach infeasible.

You could use the phrase if you liked, but each word is only 10 bits of entropy.

One nice thing about having a mnemonic for the password is that you don't have to remember the words precisely -- you can modify the mnemonic to suit your tastes as long as the prefix remains. I originally wrote it to generate passwords that I have to enter frequently (e.g. sudo), so being short was a goal.

I'm working on making actual passphrases with more entropy per word.

Yeah, I assume that you can just have a non-deterministic expansion which will add some entropy per word to increase the entropy of the passphrase over the abbreviated version, but my point was just that even if there's no increase in security by using the full passphrase, counter-intuitively, using the full phrase would likely be more convenient for me (and probably for many others).