Focus any element which makes it easy to see when focus is gained or lost, such as this textbox on GitHub
Notice that while Ctrl is held down, focus is stolen
This can lead to unintended results in apps that react when focus leaves an entry such as in Inkscape:
Create a shape on screen
Overwrite its value for height or width with your own value (but do not use decimal places). For example type in 22.
Select this value and attempt to copy it with Ctrl + C
Notice that when you press Ctrl, focus is lost which mean Inkscape converts the value to include .0 and your selection is cleared before you are able to copy the value.
This can lead to unintended results in apps that react when focus leaves an entry such as in Inkscape:
22
..0
and your selection is cleared before you are able to copy the value.