[unknown] That is the million dollar (or 35 dollar, or £5.5, or £2.8, depending on where you buy it) question. ;-)
Seems that the jury is out on this question. Some people say they see less channelling, more even extraction, better tasting shots. Others (myself included) am not sure yet. A minority said it even made their shots worse.
Common sense is that as it sandwiches the puck, it might help keep it together. This could translate to less chaneeling and more even extractions, and maybe it does - I just don’t know.
Puzzling things are also happening: people said it makes the shots run faster, and to me this is counter intuitive and a bit confusing (I haven’t paid much attention to that, so don’t have an opinion, but I don’t think it makes the shot slower, which is what my logic thinks should have happened).
I certainly haven’t noticed a negative effect on the shots, and the cleanliness benefit is definitely there for me, so I use it, at least for now.