Screenshots in macOS and Continuity Markup
In macOS Catalina (10.15) there's a new (maybe this was released in an earlier version) version of the built in Screenshot app has some really cool features that addresses most of my screenshot needs. Before continuing you should read the following Apple support articles about the built in Screenshot tool:
One thing that is a bit of a hidden gem is the ability to quickly markup screen shots both using the Markup tool. To activate the markup tool click the thumbnail icon of the screenshot (right after it's taken). The following video highlights this:
{% asset_img macos-screenshot-markup.gif %}
The Markup tool has a very cool feature called Continuity Markup that allows you to markup the screenshot either on your iPad or iPhone. The following video shows this. Note: once I clicked on the thumbnail of my screenshot, in the bottom right corner on my screen, it automatically turned on my iPad for me!
You can also use Continuity Markup when using Quick Look to preview a file (ex: hitting spacebar on a file in Finder).