Difference between bibliography management styles

Difference between bibliography management styles

There are two ways that I've seen people including their bibliographies. The first is without including any package:
% Document:
\bibliographystyle{ieeetr}
\bibliography{<file>}
And the second includes biblatex:
% Preamble:
\usepackage[backend=bibtex,style=numeric]{biblatex}
\addbibresource{<file>.bib}
% Document:
\printbibliography
What exactly is the difference between these, and which is preferred in what situation?