It would depend on the project really.
Sometimes all you need is local date/time in a simple way, and especially on small targets, you don't necessarily want to bother fiddling with code that implements going from binary to calendar and conversely, you may not have access to a working and *non-bloated* library that does so correctly, you don't want to have to deal with potential bugs, etc.
And OTOH if you're using some kind of embedded OS that already has everything to do this, binary would be more adapted. Just a thought.
I for one have never used standard time functions on small targets, I'd be curious to see how often they are available, if so, what's the code size, if they are 100% bug-free, etc.