hello i am new to dos i usually play as a tank i was just wondering are dots a must?

[papichulo123]

when i play as a monk which dots are a must for maximum dps?
when i play as a bard which are a must?
when i play as a ninja which are a must ?
when i play as a dragoon which are a must?

[Viridiana]

For any given class or job, the ones native to that class/job will be essential for maximum dps. So BRD needs Windbiter and Venomous Bite, DRG needs Chaos Thrust and Phlebotemize, etc. There are some weird levels as you're leveling up where individual dots might not be worth it, but as a rule you want to maintain dots at all times (unless the enemy will die really fast).

[Allyrion]

For any given class or job, the ones native to that class/job will be essential for maximum dps. So BRD needs Windbiter and Venomous Bite, DRG needs Chaos Thrust and Phlebotemize, etc. There are some weird levels as you're leveling up where individual dots might not be worth it, but as a rule you want to maintain dots at all times (unless the enemy will die really fast).

^ This for the most part.
But I'd say 30 second dots have a very niche spot thoughtout the leveling process. It will usually need to last maybe 21 seconds (varies individually) for it to be effective.
They find some use in Dungeons on off targets, but mostly good for Bosses.

Shorter Dots are really good, especially BRD dots - Venombite is really short and Windbite procs Bloodletter.
For potency comparisons, you can divide the time by 3 (the server tick interval) and multiply it by the potency.

For example, Mutilate starts at 18 seconds. It does 30 potency per tick.
You could say it gains 30 potency every 3 seconds then, and at 18 seconds it's 240 potency.
It also delivers 60 potency on-hit, so it's good for 300 potency in total.

You can compare this to your other moves and their potency and see how many ticks it needs to surpass them.
In general, they have a very high potency and that's why all the innate dots of a Job are worth it. They just take some time to do that damage, so if the mob dies early it's a waste.

[Kitano123]

You should always use Demolish as a Monk, Touch of Death is TP dependant. Let them drop of before reapplying them though.

[SeraviEdalborez]

DoTs are typically always better than a raw GCD, provided the enemy will live for at least 2-4 ticks of the DoT (which is not a tall order).

You can calculate for yourself. A DoT inflicts its potency every 3 seconds. So divide duration by 3, and multiply that number by the DoT potency to get DoT's total potency.

Arbitrary example, Chaos Thrust is a 250pot initial hit and a 35pot DoT that last for 30 seconds (or 10 ticks). So total potency is 250+350=600. Where a combo'd Full Thrust is 360pot.

Optimal DPS rotations in a sustained fight involve upkeeping selfbuffs, debuffs, and DoTs and filling in the empty time with your "vanilla" moves. There are a few exceptions that are highly debatable to keep up (Fracture on MNK for example), but for all class and job-native skills this is generally a truth.

[Sleigh]

when i play as a monk which dots are a must for maximum dps?
when i play as a bard which are a must?
when i play as a ninja which are a must ?
when i play as a dragoon which are a must?

For every class, you'll be using almost every DoT in their arsenal as often as possible without refreshing it too soon, with only a few exceptions (BLM Thunder spells being more specific in nature, and SMN/SCH Miasma II being quite niche and only useful in long AoE encounters or with Contagion). The only DoT I'll say steer clear of until you understand its use, if at all for the class, is Fracture ... that one, on classes other than WAR, is TP inefficient and will screw with rotations typically unless you know what you're doing.

[Skvimpan]

Most have been answered already, when to use dots vs regular gcd (like demolish vs snap) is often based on how many ticks you'll get out of it before the mob dies. Basic rule is to refresh dots just as the old one dissapears.
There is of course a lot more to this then just what "must" be up and when, for example you dont want to use ToD just before titan jumps since you wont be able to sustain GL by hitting him when he comes back since you delayed your GL refresh by 1 gcd.

Bard dots have an 50% chance on crit (for each dot) to reset bloodletter cd, so other than the potency from the dots you also have the extra dps from more bloodletters, so you should try to multidot if you have more then one target. same goes for thunder as BLM kinda, but since the proc rate there is a lot lower its more rng than bloodletter. I generally do 2x thunder 1 in UI (instead of t1, b1) when i got more than one target thats not in range of flarespam. (t9 golems, levi orbs etc).

So yea, there is more to optimizing dps then just answering your questions, so try to focus on one class and understand why you use (or why you dont) use specific skills in certain situations.

[Tsilyi]

Shorter Dots are really good, especially BRD dots - Venombite is really short and Windbite procs Bloodletter.

note: both bard/archer dots interact with river of blood at 48 to finish the cd on bloodletter. also by the time you get windbite, venomous bite duration is extended 18 seconds (the same as windbite) by the trait "enhanced venomous bite.

[Arkenne]

For example, Mutilate starts at 18 seconds. It does 30 potency per tick.
You could say it gains 30 potency every 3 seconds then, and at 18 seconds it's 180 potency.
It also delivers 60 potency on-hit, so it's good for 240 potency in total.

Had to step in for this one :/

[Allyrion]

Had to step in for this one :/

Yea, added 60 twice, my bad.