From what I know, newborn Tallbirds are very weak, get hungry all the time and follow player everywhere, making it hard to keep them alive. And after they grow into adult Tallbirds, they become hostile towards player. It also doesn't seem like they will create a nest to spawn eggs in, so it seems kind of useless and effortsome to hatch the eggs at the cost of a nice dinner. If killed, a Tallbird drops 2 meats, and while a normal Tallbird will respawn in 2.5 days, it takes a lot more to grow one from an egg.
In comparison, pigs have 250 HP and do 33 dmg, don't need food (unless you want them to follow you around). Smallish Tallbirds have 300 HP and do 50 dmg, but they require 60 food per day, each, which can be a nuisance. Pigs are better for this follower role, because they're ready to fight right off the bat, no need to wait 11 days.
Why would I want to spend so much time and resources to hatch a Tallbird egg?
Best Answer
The only real advantage of the smallbird and smallish tallbird is that some mobs don't run away from them. Birds like crows, redbirds, etc. won't fly away from them, so the smallbird can be an easy source of feathers and morsels.
I guess you could also herd them into a pen, and have your own tallbird farm.
So, to answer your question: as near as I can tell, the value is fairly limited.