Here's an interesting article on blow-by, up on the BITOG website. Interesting read, but for those who don't have the time, here's a summary:
Combustion chamber explosions force fuel, air and moisture past your piston rings and into the crankcase, causing wear, soot and deposits.
Soot and deposits are left over from incomplete combustion, and collect on sensitive engine parts such as the piston rings. Deposits include unburned fuel, moisture and sulphur dioxide. The collection of these hinder the piston ring's ability to contain pressure, encouraging blow-by.
Ring and cylinder liners wear away as a vehicle ages, reducing the engine ring's ability to maintain pressure. This causes a loss of engine horsepower, oil contamination and dilusion, inevitably having a negative impact fuel economy, due to reduced compression.
Good news is, Auto-Rx helps keep your engine free of such contaminants, helping to maintain compression and horsepower, keeping your engine at its peak for longer.
Forgot to include: byproducts slow down, and sometimes prevent, seals and rings from doing their job properly. Which is why it's important to keep your engine internals clean.