My wife has for months been trying to teach our daughter to make the sign for "daddy" by shaping her hand like the letter L and placing it against her forehead. Thankfully it's a sign the kid has yet to master, although she can practically narrate a Mutual of Omaha safari video with only her hands.
Snark if you must, but signing has saved us from some serious meltdowns. At 14 months, Emmeline can only say a few words, but she can hold a conversation nonetheless. We've found it so useful to be able to communicate with our toddler that I'd forgotten there was any signing controversy at all.
Some say it's great for babies. Some say it stunts speech development. And still others say kids should be kids, not streetside mimes.
But if I had the choice between a pre-speaking toddler screaming her head off while grunting and pointing for unknown reasons or a pre-speaking toddler who can calmly use her hands to say, "Milk please!" I'd take the latter in a heart beat. Or at least until she masters that "daddy" sign.
(Here's an awesome signing resource if you're interested.)