Demonstrates the motive for wanting the ability to have commands in the prenote of a citation command.

Biblatex-CommandInPrenote-Mwe.tex

\documentclass{article}
\usepackage{a4wide}

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@book{sep_2016_stanford,
  author = {{SEP}},
  date = {2016-23},
  title = {The Stanford Encyclopedia of Philosophy},
  urldate = {2016-06-20},
  editor = {Zalta, Edward N.},
  timestamp = {2016-11-02T19:02:26Z},
  url = {http://plato.stanford.edu/archives/fall2016/}
}

@inreference{wikipedia_2016_paris,
  author = {Wikipedia},
  date = {2016-08-01},
  title = {Paris},
  note = {Page Version ID: 732468897},
  urldate = {2016-08-01},
  booktitle = {Wikipedia, the Free Encyclopedia},
  langid = {english},
  timestamp = {2016-10-28T03:03:49Z},
  url = {https://en.wikipedia.org/w/index.php?title=Paris&oldid=732468897},
  rights = {Creative Commons Attribution-ShareAlike License}
}

\end{filecontents}

\usepackage[%
    style=authoryear,
    url=false,
]{biblatex}
\addbibresource{\jobname.bib}

\begin{document}

Entry outside main citation:\\

See \citetitle{wikipedia_2016_paris} in \autocite{wikipedia_2016_paris}.\\

Entry as a prenote:\\

lorem \autocite[Rights,][]{sep_2016_stanford}\\
lorem \autocite[See Paris,][]{wikipedia_2016_paris}.\\

Entry as a prenote, using a command inside a prenote (uncomment source):
%lorem \autocite[\citetitle{sep_2016_stanford}][]{sep_2016_stanford}\\

\printbibliography

\end{document}