Do you remember that Seinfeld episode in which George’s girlfriend constantly tells stories interpolated with “yada, yada, yada”? George feels as if he’s missing something in her stories because she resorts to this interjection without filling in the details.
In the same way, some Latin terms (such as e.g.) have become so common in English writing that we throw them in prose without really stopping to think about what they actually mean, and we assume that our readers know, too.
So, for example, you might write,
The monstrous, green octopus stretched out its tentacles and encircled the Mary Celeste, etc.
What the heck! The octopus encircled the ship and then what? Sucked the crew dry of protoplasm? Squeezed the ship into toothpicks? Gave the gang a group hug? What happened?
In writing, it is never a good idea to resort to Latin terms such as etc., et al, and Q.E.D. You may know what these mean, as well as what unimportant details you’re skipping over, but your readers won’t, and they will consider you unimaginative for resorting to these terms. Okay, so you can continue reading about the Mary Celeste’s encounter with the radioactive octopus and see that all does not end well for the crew, but why did you skip the details? Why not fill them in for the reader? Isn’t drawing the whole gory picture half the fun?
Not only that, how many people actually know what some of those Latin terms stand for? You may spend your days immersed in 18th-century philosophical tracts and can pronounce quad erat demonstrandum*, but unless the genre that you write in calls for such archaisms, your 21st-century reader (especially one for whom English is not a first language) may be confused. That precious Latin term you’ve just used may trip your reader up, waking her from the spell of your story and sending her to the computer to look up N.B.**, at which point she’ll get distracted by cat videos.
So, yada yada yada, the upshot is to always do the legwork for your reader. Skipping details or using unfamiliar Latin phrases annoys and frustrates your reader, and personally, I would rather look at cat videos than be frustrated, viz.*** by fussy language.
*”Which was to be demonstrated,” or Q.E.D.
** “Note well,” or nota bene.
*** “Namely,” or videlicet.