LOL
I just started thinking for example:
I trade intraday, a typical move might be X pts or pips, call it 100, for sake of argument. You get a good move in your favour, say 30, price starts to retrace, or it gets to an area of S/R etc. You want to secure some profit, so you sell half for sake of argument.
Now you've only got half of your position on, price just has to move so much further to make much impact in terms of good profits.
Like I say, definitely not saying it's wrong, just depends on your style and what works. And yes, if you need to take some off the table to feel comfortable, that can actually be a legitimate reason for doing so.
My research told me it wasn't helping - I wasn't doing it for a legitimate reason. But equally, somebody could have a method whose success depends upon them securing some profit,for example, and leaving the rest to run with a stop at or near break even.