pros & cons of milling head to .040?

[club_bust]

i'm thinking of milling my sohc vtec head to .040 to raise the compression. my uncle told me that in order to raise my compression i would need to get higher compression piston as well in addition to milling it, is this so? how high of compression would this raise my compression? he also told me that this would alter the timing bout 3-7 degrees, is this so?
what are the pros and cons to this "cheap" power gain?
thanx.

 

[Declectic]

pro - raise C/R
con - irrervsible mod

 

[tdb81]

pro: raise compression
con: throw off valve timing (can be fixed with adjustable timing gear) you probly wont notice much of a difference though