Sometimes StackExchange sites permit on-topic, soft question, community wiki answers, if they're constructive and interesting enough to the community. I hope this fits.

I'm wondering moments in your TeXing career you learned something

• that saved you a lot of time
• led to production of nicer documents

I will post my example that inspired this question and hope to learn useful facts.

• Always ask yourself, is this package a tool or a prison? – John Kormylo Sep 25 '16 at 22:44

For the categories

• that saved you a lot of time

my answer is automation tools! These save me a lot of time and thinking as they automatically compile the needed number of tex runs and the bibliography.

• for quick documents, like for answering questions on this site, my tool of choice is latexmk
• for more complex projects I found ltx2any very comfortable to use
• and ultimately for a maximum of possibilities and control I love to use arara

For a more exhaustive list of available tools, see Tools for automating document compilation

On math.SE many people are missing good uses of \left and \right.

(\frac45)


v.

\left(\frac45\right)


More detail here: "(" or "\left(" parentheses? (IMO just using \left and \right in simple situations is often an improvement).

Following through to link in comment: The package nath seeks to obsolete this. Even better (but I've never used it so cannot offer an example at this time).