[Aser]

When I learned to touch type a few years ago, I found it really useful having the letters on the keys so that when I messed up I could look down and make sure my fingers were in the right places and get going again quickly. Eventually after a week or so practicing, I had the hang of it and no longer needed to look at the keys. So I'm not really sure what blank keycaps achieves.

[piptastic]

I use a blank keycap keyboard. There are little raised dots on the F and J keys to find your placement without looking down.

Two reasons to use one: 1) security - slows down most people when “borrowing” your computer. 2) looking cool and being able to joke that it used to have keycaps but you type so much that they all wore off

[MivLives]

I think the argument is if you can't look down you work harder at remembering it because that easy reference isn't there.