While Substitute is useful and IsMatch (and friends) are helpful, neither of them are helpful when you need to complex search and replace operations.
For example, I'm currently working with an output file that has particular constraints around the characters used (7bit only) and limited line lengths (80 characters). While I've managed to get through most of it, it would be so much easier if Substitute supported RegEx, or if Match/MatchAll supported replacements.
And the bit I haven't found a workaround for is line lengths, sure I could chunk it based on number of characters, but then you get line breaks in the middle of words, so I need to only break on spaces... (e.g. the last space before 80 characters)
I can figure that out in RegEx, I can't find a way to do it in Power Apps.
I don't want to have to resort to buying Plumsail's Documents connector, which brings RegEx support to Power Automate... It's just not cost-effective for my usecase.