What's the deal with finger sleeves on gloves?

[bbrages]

My son has it in his head that he wants a glove with a finger sleeve.

What's the deal with them? Apparently, they are used mostly by pitchers? Cause you're going to give away your pitch with your glove hand index finger... ???

[TexAg]

i thought they were to conceal the pine tar?!

[baseball007]

They are to keep a fielder from breaking/jamming his finger when he dives.