The need for excessive escaping of text can slow down typing considerably, so it's good if the markup is CollisionFree.
Fast to type also means keeping the markup "linear" rather than "two-dimensional". For example, using parenthesised syntax to delimit block of text:
( some block of sample text )
you make it faster to type than by using indentation or markers on every line:
: some block : of sample : text
This becomes especially important when the text is not typed, but rather pasted and then the markup is added.