For PvE, a "click cast sequence" is close to optimal single box dps, and can be boxed as easily.

With a normal cast sequence, you have spell 1, then spell 2 etc.
There's a bit of latency, because you send to the server cast this spell.
And then wait for confirmation from the server that the spell is finished.
Before going to the next spell.
Depending on your milliseconds of latency, this can be bad or not.

With the click sequence, a master macro calls several other macro's.
Since each sequence does one spell and then is a series of comma's (no actions)...
You don't need to wait on the server for confirmation a spell is done, before moving on to the "do nothing" portion of that sequence.
However, the other sequences are also all running simultaneously.
It is marginally faster then a normal /castsequence (1x your latency, instead of 2x).

But you can prioritize your spells (each tries to execute at once, but top down or earlier macros called in the master sequence has priority over later macro's).
Further, with the correct number of comma's for your spam speed, you can time how long until each portion is recast.
That's the largest strength of the click sequence.
You can have it cast Corruption, then Agony, then Immolate, then Conflagrate, then Incinerate as the fall through.
With the right number of comma's, it will recast Corruption first, even if Immolate has also expired.
You'll never get a Conflagrate cast, while Immolate is not up, because Immolate occurs first.
That assumes you have the right number of comma's for timing.
The last "fall through" spell is spammed, if you're on comma's (no action on this click because everything is either still ticking or on cooldown), so Incinerate will only go while Immolate is already up.
If Immolate expires, you won't be spamming Incinerate, the comma's of timing will have you recast Immolate instead.



Within the default action bars, you can Shift 1 and Shift 2, to switch between two bars.
The other bars, Shift 3 through Shift 6, can be displayed in interface options.
But that gets you 12 keys which can vary easily.