We're continuing on our topic of writing quality WordPress themes by looking at the Theme Check plugin.
Theme check was originally developed to give people writing themes for the WordPress.org repository a way to check their themes for compatibility with the theme review requirements before they uploaded their theme for review.
If you're not aware, when you upload a theme for review it's run against a series of automated checks to see if the theme meets the best practice guidelines established by the theme review team.
What does it do??
As stated above the Theme Check plugin runs a series of automated tests against your theme that look for things like depricated functions and required CSS classes (.sticky, aligncenter, .bypostauthor...).
Even for Clients?
While it's true that for client work you have a solid idea of what they are going to be doing with their theme the fact is that we all miss stuff from time to time and Theme Check can help make sure we've accounted for everything we should.
I think that everyone building WordPress themes in any capacity should be running their themes through Theme Check during development to ensure their providing clients with top quality service. You may decide that due to requirements of the current project you're going to skip some of the recommended items on the list but at least you'll have accounted for accepted best practice in WordPress theme building.