Difference between bibliography management styles

Question

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?

Answer 1

\addbibresource is a biblatex-only command. The main (only?) difference to the traditional \bibliography command is that biblatex/biber do not exclusively work with .bib files but allow for other bibliographic formats. That also explains why \addbibresource insists on the file suffix.