Consider the following MWE:
\documentclass{article}
%\usepackage[T1]{fontenc}
\begin{document}
\textbf{\textsf{Some text}}
\end{document}
The output of the above code is
and doesn't change if I uncomment the line
%\usepackage[T1]{fontenc}
Consider now the following MWE with scrartcl class instead of article:
\documentclass{scrartcl}
%\usepackage[T1]{fontenc}
\begin{document}
\section{A section}
\textsf{Some text}
\end{document}

Uncommenting the line
%\usepackage[T1]{fontenc}
you get

As you can see, the sans serif font of the title is less bold than without fontenc, while the normal text is not changed.
Does fontenc, combined with a KOMA-script class, load a different sans serif font, but only for bold face?

SFSS(cm-super) is loaded. So yes, there are different sets loaded. Packagelmodernis quite similar and gives you excellent support for latin scripts including many extended accented letters. – Johannes_B Feb 07 '15 at 18:41articleclass? – Sterry Feb 07 '15 at 18:56