Somebody may disagree.. however.. this is per my own experience..
My EGR pipe was 99% clogged when it had 150k miles. Of course, I do NOT know when it started being clogged but I found it being clogged at 150k miles.
Then, of course, I tried real hard to remove all those shoots and gunk as much as possible. I f I had a sort of parts cleaner or something, it wouldn't cause me such sweat... It was really hardened.....
I confess that I had been using the cheapest available gas 87 octane or something... No other additive ever...
Anyway, after I removed like 70~80% of shoots inside wall of the pipe, I reinstalled with fresh gasket... then, what a difference!!!! It became reall smooth...
Now my 94 L sedan has 196 k miles... I still use the lowest octane.. but it runs super!!! Actually, it feels like it runs better than my 95 LS Coupe with 135k miles, which I have never opened EGR area... I hope I can do EGR cleaning for 95 LS Coupe someday... but I know it is not really easy, very time consuming due to its' confined work-area....