Impact of Ferrite Chokes on power and signal

I wanted to get the collective wisdom about use of ferrite cores on
power cords.....and also in the signal path. I just ordered
a bunch from:

I also ordered a couple of these to try on the output of each
of my monoblocks:

I figure i'll do a lot of a/b comparisons with and without
ferrite in various spots...but i'd be very interested opinions of other tweak geeks!!!
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They work well if you know what your doing with them. Cardas uses them in there top of the line power cords and interconnects, but they been doing it for years and know how and where to use them.

I tried the clip on ferrite once, and the sound just went dead and dark. so there you go.
Phillyb: do you have any suggestions about how to best use ferrite cores?
Is it true that ferrite eventually gets "saturated" and at that point of no use?
I think my system sounds better with the ferrite in place. I'm not hearing much, if any roll off of the highs, but the bass is tighter, and image is more stable. I ended up using the maximum amount of ferrite on each clarifier. Unfortunately, It's not easy to do blind a/b testing with this...which is what I consider to be the gold standard for testing tweaks. But if my ears are right, I'm hearing some important improvement.
"Sakti" "on line" is a pretty good brand. I use one on my Sony W222ES CD recorder It knocked off the digital glare I was getting. I placed it on the power cord just where the cord enters the unit. If you have a Digital component that sounds bright they can help. Best thing is to experiment. Try it both ways. What "Elizabeth" said is true... I have never tried them on ics. Tried one once on my ARC VT50, made it sound dead, yuk! The Audioquest power cord I use on my Arcam Alpha 9 has a AQ tpye on the end just before the plug, into the unit. It gives the Arcam a more "analog" warmer sound.