Initially I wanted to open a question:
How to get (more) text on a page with large floats?
But of course the topic at hand has been covered way more many times than google can list on one page. (some links: /1, /2, and /3). After searching around, I started adding the following lines in my MWE which essentially solved the problem in the MWE:
\renewcommand\textfraction{.1}
\setcounter{totalnumber}{5}
\renewcommand{\floatpagefraction}{.8}
Picture for MWE

So I am in the situation where my MWE works perfectly while my real document does not. The relevant page in my real document looks like this:

=> I am wondering, if I play around with the values mentioned earlier, could I break something? Are there values which I should not use for textfraction, totalnumber or floatpagefraction?
MWE
\documentclass[
a4paper
]{scrreprt}
\usepackage{
lmodern,
}
\usepackage[%
paper=a4paper,
left=3cm,%
right=2cm,%
top=3cm,%
bottom=2cm,%
headheight=1.5cm,%
headsep=1.5cm,%
]{geometry}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\renewcommand\textfraction{.1}
\setcounter{totalnumber}{5}
\begin{document}
\begin{figure}[htbp]
\centering
\fbox{\parbox[c][8cm]{0.4\linewidth}{Height8cm}}
\caption{Test}
\label{fig:Test1}
\end{figure}
Short text. Blahblah. Short text. Blahblah. Short text. Blahblah.
\begin{figure}[htbp]
\centering
\fbox{\parbox[c][10cm]{0.4\linewidth}{Height10cm}}
\label{fig:Test2}
\caption{Another test}
\end{figure}
Third short text. Blahblah. Short text. Blahblah. Short text. Blahblah.
\begin{figure}[htbp]
\centering
\caption{Test}
\fbox{\parbox[c][6cm]{0.4\linewidth}{Height6cm}}
\label{fig:Test3}
\end{figure}
\end{document}
\textfractionto anything less than0.2. If less than 20% of the page is available for text, the little amount of text that can fit on the page tends to look totally forlorn, and the likelihood that the text on that page actually contains a call-out to the figure(s) and table(s) on that very page is rather low. Put differently, it's advisable to create a floats-only page if the floats take up at least 80% of the height of the text block. – Mico Jul 22 '14 at 08:34