I was just messing around in LaTeX with the libertine and libertinus packages, and noticed that switching from LaTeX to XeLaTex to LuaLaTeX all produced PDFs that were mostly the same length, except spacing in paragraphs slightly changed.
What is causing this? Is there any “correct” output?
At first I thought it had to do with the fact that libertinus switches from Type 1 encoding with pdfLaTeX and OpenType with XeLaTeX/LuaLaTeX (not sure if libertine works in the same way), but even the outputs from XeLaTeX and LuaLaTeX are different.
\documentclass{turabian-researchpaper}
\usepackage{biblatex-chicago}
\usepackage{turabian-formatting}
\usepackage[pass,letterpaper]{geometry}
\usepackage{libertine} % or libertinus %
\begin{document}
Afraid of intimacy, we use technology to remove ourselves from the real world because we
believe more will listen to us when we are online. The internet and our phones become an
addiction that is hard to break. Although our technological habits change our personal
relationships for the worst, we continue the cycle of needing to text or post to social
media to feel validated. We have been blinded by our own emotions into thinking we need to
be online so we don't have to self-reflect, even though the situation is the opposite. This
is extremely harmful to our social skills, and we form habits that, before technology, most
would have called awkward or antisocial. We sit with our friends without interacting. We go
to cafés alone to do nothing but text. We spew hateful comments online through the barrier
of anonymity. However, the habit of checking your phone, posting to social media, and
commenting on content is extremely hard to break and needs patience and the willingness to
take breaks often. Technology does not need to always be wasting resources in the back of
your mind.
\footnote{Before you start an unrelated argument, I'm not actually anti-technology like
this might suggest. This was an essay written to appease an English teacher.}
\end{document}
Sorry if this isn't minimal enough. I couldn't find a way reproduce the issue without these words and packages.
This GIF demonstrates the differences between pdfLaTeX, XeLaTeX, and LuaLaTeX. 
(Added by David Carlisle) test file just using article class but the same width and font settings as in the original example, it shows the same three output variants for pdf/xe/lua latex as the original but has less dependencies so a bit easier to trace (perhaps)
\documentclass[12pt]{article}
\usepackage{libertine} % or libertinus %
\setlength\textwidth{469.755pt}
\setlength\parindent{36.135pt}
\addtolength\oddsidemargin{-1cm}
\begin{document}
\typeout{\the\font}
\typeout{\the\fontdimen2\font} % space
\typeout{\the\fontdimen3\font} % stretch
\typeout{\the\fontdimen4\font} % shrink
\typeout{\the\fontdimen7\font} % punct
Afraid of intimacy, we use technology to remove ourselves from the real world because we
believe more will listen to us when we are online. The internet and our phones become an
addiction that is hard to break. Although our technological habits change our personal
relationships for the worst, we continue the cycle of needing to text or post to social
media to feel validated. We have been blinded by our own emotions into thinking we need to
be online so we don't have to self-reflect, even though the situation is the opposite. This
is extremely harmful to our social skills, and we form habits that, before technology, most
would have called awkward or antisocial. We sit with our friends without interacting. We go
to cafés alone to do nothing but text. We spew hateful comments online through the barrier
of anonymity. However, the habit of checking your phone, posting to social media, and
commenting on content is extremely hard to break and needs patience and the willingness to
take breaks often. Technology does not need to always be wasting resources in the back of
your mind.
\end{document}
turabian-formattingpackage: you don't need to (nor should you) specify\usepackage{turabian-formatting}. Simply loading theturabian-researchpaperdocument class will create a turabian-formatted research paper.