Especially when I'm asked to work with sdlxliff files, I see many segments beginning with spaces which are inserted as placeholders.
PowerPoint files are full of them.
I'm not bothered while translating, and I don't want to take to time to add the fragment (without those leading spaces) to my TM.
So, after it's over, I'd like to remove all of these unnecessary spaces from my horizon.
You can use the regular expression \A to indicate segment start and \s+ or perhaps (\s)+ to mark a range of spaces. Then replace by nothing.
Replace: [leave empty]
Tick the checkbox regular expressions
And you can use \z for segment end