I don't think it's a huge issue, but what the point of is when you want to use a non-websafe font, then you've got to use one of these font replacement schemes. And those don't do subpixel rendering. And so you'd use this. Presumably.

You certainly wouldn't use it for text that is websafe, like Georgia, because yes, the operating system can do its own subpixel rendering in that instance.

The whole "sub-pixel rendering" is getting out of hand. Text on Apple systems look the way they do for several reasons, sub-pixel rendering might the tech-sexiest of them, but it's really only a minor benefit, almost totally meaningless at the size of header text.

Because Apple's is the only OS that gets this crucial bit right?

But it's not crucial. I'm perfectly happy with whatever text rendering my browser uses. I can read the results, and that is sufficient. Just let my browser render your text in accordance with my dictates, and don't try to interfere. You're less likely to break things that way.

It is crucial if you spend much time staring at a screen. Bugged font rendering is distracting and hinders readability.