Is it counter productive to workout if you are still sore ..

i've worked out steady for the last 2years rarely missing even 1 day of
a 3day workout week.

monday we changed up some chest exercises and started doing declines/
and some negatives (which i have never done in the 2yrs of working out).
Well it's friday and I am still sore in my pecs from mondays workout.
But not real real sore.

I have been told that if you are still sore you should not work out
because you are basically never letting the muscle heal in order to rip
it again. Is this true? I figured the 4 days of rest on that muscle
group should have been more then enough.

I also have another question about DOMS, but I can post that at a later
time.