I used them "back in the day" before I knew much about them. As mentioned above, they don't affect the lower frequencies, since the sound waves of the lower frequencies have greater length than the width of this foam. But hey, if you're in a home studio, they may work okay, esp. if there are no low freqs to worry about leaking through.
On the flip side, with a little work, you can construct your own sound baffles, as I did, out of compressed fiberglass, covered with various materials - either 4 or 6 inch thick is what I've used in my home studio, and it works quite nicely.