Kinda depends- I think a lot of the methods listed in this thread either work well situationally (i.e. posting to reddit is a lot more productive with standalone comedy strips as they flourish there as long as the content is solid) or in some cases may be a better time investment once you have a larger starting fan-base.
Something like an animated short I view like this: If you don't have many readers to begin with then the point is that you're still self advertising your work, which is basically an unknown IP, out to strangers. First of all it's the author shilling their own product, which is a necessary evil, but similar to what we do when we create single image adverts. Then if the video doesn't seem to be popular already it might garner some skepticism ("huh it's only got like 2 likes and 100 views, I wonder if it's actually any good?"), and then you're also advertising a still image medium with a fancy video presentation so even if people go to check out the comic they'll have the animation to compare it against in the back of their mind, and so the comic had better be pretty phenomenal and hold up~ All of this can generate readership but it's far from a guarantee and at the end of the day you spent TONSSSSS of time on this animation that for your level probably had a similar effectiveness as a fancy promotional poster or something.
Compare this to an established creator with a few successful projects under their belt and an established readership. They make a short animation to announce an upcoming project of theirs, but chances are it'll get a decent amount of likes and several views from the established readership that they already have. Now when new people see the video, they'll think "oh wow, this has 300 likes and a few thousand views, let's check it out~" Not to mention they might get a number of shares and retweets on the post- which in my experience I'm more likely to take something at face value that a friend shows me than some random targeted ad from a company, personally. As for the content of the video itself, fans already know what to expect from the author, art-wise, so there's not a huge expectation hurdle to clear on what the animation shows vs. what the actual comic shows.
Now of course, the above scenarios are completely hypothetical and the newbie creator might strike gold and the established one might have their animation flop, but I think it rings somewhat true. Like the video I mentioned commissioning in my original reply- I spent 2 or 3 weeks coordinating it with the producer and it wound up getting a whopping 64 views after like over a year xD I could have spent those same 2-3 weeks just making a few nice promotional images or posters and likely gotten the same or more effect. But the video was fun so no regrets~