CSS Pie & IE Meta Tag

CSS Pie & IE Meta Tag

I've been using CSS3 Pie on my site with great success. I recently had a
Jotform form with a custom CSS button with radius, Pie doesn't work with
Jotform so I came across this meta tag
<meta http-equiv="X-UA-Compatible" content="IE=Edge" />
which when added to the particular page resolved the radius issue in IE8.
My question is this, if it's this simple to allow older versions of IE to
render modern CSS can this tag be utilized as default and if not why not
i.e bad practice, technical reasons etc.
It seems to good to be true so I'm guessing there has to be a reason, I'm
aware it doesn't validate but to avoid this it can be added to an
.htaaccess file.