Well, not immediately, but it shows its effects after a few minutes. Let's say in our GNB example, we have a NIN in our party who uses Trick Attack on point everytime it's ready. We want our buffed Blasting Zone fit into this TA window. This will go well for the first 4-5 min, but it will be difficult to hit it every 60s in a 10s window because we clip/hold Blasting Zone for ~1s everytime it comes off CD because of GCD recast (optimal 2.4s). There is actually a Voidwalker speed run where a GNB started their first BZ at 0:10, and their 11th at 5:19!
Another example is WAR, and Upheaval: It's also because of our GCD that we hold Upheaval for ~1⁄3 GCD every 30s. That means if IR (90s recast) is used exactly everytime it's ready, Upheaval drifts 1 GCD behind everytime we use IR. So, 1st IR Upheaval is used after 1st FC, 2nd IR it's used after 2nd FC and so on. Yet, if we do not delay IR one bit (which ofc we dont want that to happen) at our 5th IR Upheaval would fall behind the 5th FC and thus wouldn't be inside IR anymore.
So, the question remains: do we delay our GCD to keep our oGCDs aligned? Keep the GCD rollin' and misalign our oGCDs with our buffs? Or delay our buffs, so that our CDs align once more?
Either way it's a loss, and that is when SkS/SpS starts to hurt instead of being benefical.
I know it's a little exaggerated as the effects show themselves after minutes of '100% uptime fights', but I hope you get the picture and what I was trying to suggest here.