[css-flexbox] performance concern over align-items: 'stretch' as default value

Just curious at to why it was determined that the default for 'align-items'
should be 'stretch'?

I am doing my first site using a Flex framework with Table-cell(s) fallbacks
and,  I have many instances where the vertical stretch is not needed
especially if it only consist of one nowrap row. Hence me thinking to
default my main flex class to "flex-start" instead. I was a bit surprised
seeing 'stretch' as default.

Isn't that an unnecessary overkill performance-wise for those who are not
aware?

I just want to raise that concern in correlation with the following article
mentioning a 2-pass when align:stretch is involved:
http://updates.html5rocks.com/2013/10/Flexbox-layout-isn-t-slow

I am thinking a 'flex-start' default might be more appropriate.