Strikethrough: If a mob dodges, ripostes, parries - strikethrough - gives you that small % chance that your attack will hit instead of being avoided.
Reference: I highly recommend you read
THIS because it answers alot alot alot of those common questions about combat effects and the stacking limits, caps, etc.
Note: Strikethrough is only useful when attacking the mob from the front (i.e. MA / Tank could benefit from this) For everyone not the MA / Tank they should be attacking from the rear flank anyway, so strikethrough isn't going to help them in most situations.