# explicitly setting the a4paper option has no effect using scrreprt?

I compile the following code:

\documentclass[a4paper]{scrreprt}

\usepackage{lipsum}

\begin{document}
\lipsum
\end{document}


with pdflatex. If I leave out the a4paper option and compile again, the produced pdf will be exactly the same in terms of layout. Additionally, both times the log file states the following:

Package typearea Info: These are the values describing the layout:
(typearea)             DIV  = 10
(typearea)             BCOR = 0.0pt
(typearea)             \paperwidth      = 597.50793pt
(typearea)              \textwidth      = 418.25555pt
(typearea)              DIV departure   = -6%
(typearea)              \evensidemargin = 17.3562pt
(typearea)              \oddsidemargin  = 17.3562pt
(typearea)             \paperheight     = 845.04694pt
(typearea)              \textheight     = 595.80026pt
(typearea)              \topmargin      = -25.16531pt
(typearea)              \headheight     = 17.0pt
(typearea)              \headsep        = 20.40001pt
(typearea)              \topskip        = 11.0pt
(typearea)              \footskip       = 47.60002pt
(typearea)              \baselineskip   = 13.6pt


The conclusion I draw from this is that the a4paper option is the default in scrreprt and therefore it is generally not necessary to use this option when dealing with this class. Is this conclusion valid, and if so then why do a lot of people still use this option although it seems to be redundant?

The option a4paper could be omitted with scrreprt, since this is a predefined setting for all KOMA-Script classes.
Including a4paper makes the switching to another documentclass that does not have a4paper as the default easier. It also makes it easier for other people that use a given Latex code as a reference to see where and how the paper size would be changed.