Why do they advise to avoid flagging ( and in turn, chording) ?

I probably gave myself this bad habit of flagging and chording from the very beginning when I started playing minesweeeper - and got used to it.

But I also heard that giving up flagging may take a while to get used to, but it may also make you faster in the long run.

I mean, I get it - if you do not flag, you are basically avoiding hitting the squares you do not need to hit, and in turn reducing the number of clicks.

I did try that a couple of times - but I found that I need to think a lot more when playing without flagging, and the "useful" patterns (1-2-1, 1-2-2-1 and stuff like those) are not really useful there.

Thoughts?