How would you clean a messy dataset in Excel?

First decide where: Power Query for anything repeatable, formulas only for one-off work.

Typical steps are trimming whitespace, fixing dates stored as text, splitting combined fields, standardising inconsistent categories, removing duplicates, and unpivoting wide data into tall.

Power Query does all of this as recorded steps, so the same cleanup replays on next month's file. That repeatability is the main reason to prefer it over manual find-and-replace.