The following commands are physical commands. Avoid at all costs. Every use of one of these commands within a document is a failure to use proper logical LaTeX (you know who you are). Instead, think why you want the effect, and then code the logical reason, not the physical command.

• \\ (except inside a special environment like tabular, array, or verse)
• \textbf or \bf (usually need \vec or sectioning like \paragraph)
• \texttt or \tt (usually need a verbatim environment, or \url command)
• \textit or \it (use \emph)
• \textsf or \sf
• \mathrm or \rm (use \operatorname{} for math symbol, or \text{} for English)
• \mathscr (as it is hard for a reader to distinguish between I, J and T, and between C and O---use \mathcal instead)
• \tag (except where absolutely necessary, and even then take a cold shower before deciding)
• \eqno
• \dfrac
• \displaystyle
• \hspace
• \vspace
• \limits
• \noindent
• \newpage
• \clearpage
• \linebreak
• \pagebreak

If you 'know' that what you need involves one of these commands, then define a logical new command in a style file. The new command implements the physical appearance you desire, but within your document you only invoke the logical command.