Barring some optimisations being turned off to debug, there won't be a performance benefit to using cont.begin() (or getting a pointer to the first element, or whatever) unless someone's provided a really weird implementation! Pretty much all implementations (and certainly those with STL) are wafer-thin and melt in the compiler's mouth.
The plus-side is in the "or whatever" above: The same code works across different collection types whether another from the STL, or arrays, or some bizarre collection by a third party if they thought to supply a specialisation of begin for it. Even if you never use that, begin() is well-known enough that there should be a familiarity benefit.
