I think it does have quite a bit of impact...but I guess it depends on the way you use it; if you use it in such a way that that is the is only reason you're using it, then yeah.
Nobody corrects PartyWolf when he says "GIs in SCV guard impact both mids and lows?" In every other game there's been a high-mid GI and a mid-low GI. The fact that SCV's GI covers all three hit levels has very little impact. You rarely ever need to cover both highs and lows at the same timing.