Beginner's Overview to Tanking in FFXIV

[Legion88]

For example 2 CDs, each 10% mitigation.
1. Both seperated:
100-10%=90
100-10%=90
So you mitigate two times 10%.

2. Both stacked:
100-10%-10%=81
100-10%=90-10%=81
So you mitigate one time 19%.

Over the duration of the CDs it is mostly superior to chain CDs instead of stacking.
This counts mostly for teashpulls. On bosses and Savage it can be or is usually likly to stack CDs in order to survive tank busters.

[Hierro]

For example 2 CDs, each 10% mitigation.
1. Both seperated:
100-10%=90
100-10%=90
So you mitigate two times 10%.

2. Both stacked:
100-10%-10%=81
100-10%=90-10%=81
So you mitigate one time 19%.

Over the duration of the CDs it is mostly superior to chain CDs instead of stacking.
This counts mostly for teashpulls. On bosses and Savage it can be or is usually likly to stack CDs in order to survive tank busters.

There is some truth to this but largely I disagree. For example, take a look at warrior. Thrill of Battle is made more effective when paired with defiance, and more so when paired with a traditional mitigation % CD.

But even so, what you're refering to is getting the absolute most out of every defensive CD so no % of mitigation is gone to waste, and there's nothing wrong with that, but it is far more pragmatic to call upon the most mitigation when you need it. Using your example, you will need 19% mitigation for when there's 8 mobs, and not 10% when there's 3.

Still, there are ways to stack CDs effectively and ineffectively. For PLD, it'd be wasteful to stack rampart with sentinel while you're in shield oath. At that point, rampart's 20% would be reduced to 9.6%. However, stacking anticipation can and should be done with every CD at the start of every large pull. Its short 60 sec CD and 30% parry rate is applicable no matter how much mitigation is currently active. Convalescence will always make healing a large pull easier no matter what other CDs are up, and there's no diminishing returns on that.

When I do EX roulette with WAR, I will use ToB, convalescence, anticipation, rampart for one pull. The next large pull I'll use vengeance, RI+awareness for the other, where I actually do chain anticipation after RI. I aggregate my CDs in a way that creates synergy so none step on each other's toes.

[Legion88]

snip

You are right. There are defensive CDs who have a synergy with another but i was only talking about pure %mitigation.
If you just stack up %mitigation you have diminishing returns. You can circumvent this by combining them with another non%mitigation CD like your own examples, you combine diffenrent types of defensive CDs, %mitigation, HP+, healing+.
Also Anticipation has a very short CD, which makes it available on almost every pull, so you can't really lose anything in using it.

In the end it is less usefull to stack %mitigation CDs if you can circumvent the diminishing returns by just using a defensive CD which is not just plane %mitigation.