Question

That’s a pretty major difference. This
is why it’s always strongly
recommended that you use unitless
numbers if you’re going to set a
line-height on something like the
html or body elements, or indeed on
any element that is going to have
descendant elements.

http://meyerweb.com/eric/thoughts/2006/02/08/unitless-line-heights/

So now i will follow this suggestion. but is there any cons to follow this?

Answer 1

but is there any cons to follow this?

I can’t see any. The behaviour he describes:

So what’s the difference? When you define a united value, like 1em, you’re setting things up to pass along the computed result to any descendants. For example, suppose the following CSS is applied to a document containing the following markup fragment:

Is usually what you want. There may be exceptions with some typographically very specialized designs with fixed line-height s to achieve some sort of effects. But that will be rare, and you’ll recognize them when you see them.