What is wrong with this ToC and all the overfull boxes?

This code gives me a lot of Overfull hbox messages in the console, and I’m wondering why:

documentclass[11pt,twoside]{book}
usepackage[T1]{fontenc}
usepackage{lmodern}
usepackage{microtype}
usepackage[total={6.25in,10in},left=1.25in,top=0.5in,includehead,includefoot]{geometry}
usepackage{lipsum}

usepackage[titles]{tocloft}
    renewcommand{cftdotsep}{2}  %  Points spacement.
    makeatletter  % To fix a spacing problem with page number.
    renewcommand{@pnumwidth}{2em} %
    makeatother
    setcounter{tocdepth}{2} % 3 to add sub-sub-sections to ToC.
    
    % Chapter spacement:
    renewcommand{cftchappresnum}{chaptername }
    renewcommand{cftchapaftersnumb}{newline}
    setlength{cftchapindent}{0em} % Spacement to left of chapter number.
    setlength{cftchapnumwidth}{0em} %
    
    % Sections spacement:
    renewcommand{cftsecpresnum}{hfill} % quad
    renewcommand{cftsecaftersnum}{enskip} %
    setlength{cftsecindent}{0em} %
    setlength{cftsecnumwidth}{4em} %
    addtolength{cftsecnumwidth}{0em} %
    
    % Sub-sections spacement:
    %renewcommand{cftsubsecpresnum}{hfill} %
    renewcommand{cftsubsecaftersnum}{quad} %
    setlength{cftsubsecindent}{4em} %
    setlength{cftsubsecnumwidth}{4em} %
    addtolength{cftsubsecnumwidth}{0.5em} %

begin{document}

frontmatter 

microtypesetup{protrusion=false} % To fix extra dots in ToC
tableofcontents
microtypesetup{protrusion=true}

mainmatter

chapter{Chapter Title}
setcounter{page}{12}
lipsum[2-4]
section{Section Title}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
section{Section Title}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]

chapter{Chapter Title}
setcounter{page}{850}
lipsum[2-4]
setcounter{section}{12}
section{Section Title}
lipsum[2-4]
setcounter{subsection}{15}
subsection{Subsection}
lipsum[2-4]
section{Section Title}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]

setcounter{chapter}{12}
chapter{Chapter Title}
setcounter{page}{1311}
lipsum[2-4]
section{Section Title}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
section{Section Title}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
setcounter{subsection}{14}
subsection{Subsection}
lipsum[2-4]
setcounter{section}{15}
section{Section Title}
lipsum[2-4]
setcounter{subsection}{12}
subsection{Subsection}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]
subsection{Subsection}
lipsum[2-4]

backmatter
pagestyle{plain}

end{document}

For example:

Overfull hbox (0.88777pt too wide) detected at line 19
T1/lmr/m/n/10.95 13.16.14

Are these messages a sign that I’ve done something wrong with this code? What am I doing wrong with this ToC? How can I fix all these overfull box messages?

Or may I just ignore the messages and go along with that code? And what age is the captain??