I raised my compression on my 2.4L Neon and I can say without a doubt it is probably the best modification I've done to this motor, and it is very cheap only cost me $40.I think that anyone that ever has to change a head gasket should look into this, you'll have to pull your head anyway and milling doesn't cost much.

What do you have to do to prepare for changing ratio?
First off you have to have the head off. Then clean the head very well, but do not use anything that will harm the flatness of seal surfaces like the head to block, intake and exhaust manifolds to head surfaces, be gentle. Now depending on how much you want to take off will determine if you have to remove the valves. I took off .025 and didn't need to remove the vavles but only had .003 clearance from valves. But that will vay from head to head.

What is compression ratio?
Is basically the ratio at which your displacement is compressed.

Does raising compression ratio add power?
Yes, raising compression ratio is one of the easiest and cheapest ways to add power.

Does raising compression harm the motor?
Not if done properly and if you don't go over-board. Raising compression ratio normally means having to use high octane gasoline. But normally the motor will run much smoother after a compression rise.

Why does raising compression ratio make more power?
It is very simple, lets say that your compression is 140 psi and at ignition of fuel, combustion chamber psi raises to 1200 psi. If you raise compression ratio say 1/2 point, your compression psi is now 150 psi and at ignition of fuel, combustion chamber psi raises to 1300 psi. Basically works in the same way as a turbo but not nearly dramatic of a change.