Personally I'd only use the Shockwave glyph if there was some form of non-stop adds in a long fight. At short fight times (5mans) the glyph does little.
If you Shockwave once every 20 seconds (3 times per minute) and think glyphing would help, you can Shockwave once every 17 seconds (3.5 times per minute, but realistically that's still 3 times a minute as you can't have half a Shockwave execution) and unless it's being used on cool down without downtime I don't see a reason to glyph for it.
Jalousie: Two ovaries walk into a bar.
"Hey, can we get some cervix over here?"