Or should I just let them up? This is for open world mainly. Event bosses, etc....
You should shatter your clones whatever you play if you are a mesmer. The question is not to shatter or not the question is: WHEN do you shatter them.
So to answer that I should know what weapons/build you are using because condi mirage in open world isn't something very common with some specific known build or something (power mirage with gs is very good at open world farming/tagging mobs tho).
However there is a general answer that will work nearly all the time: shatter with your f2 if you know you gonna instantly replentish 3 clones again (for example you have 3 clones, you summoned 2 phantasm that will become clones in a second, shatter before they do, or those are just lost clones and lost damage). But it is just a brief answer, there are many other things to consider: maybe you need to break a breakbar, invuln etc...
Anyway if you aren't going to shatter your clones you are missiong out much. Mesmer is about shattering whatever playstile you chose (chrono, mirage, core, condi or power doesn't matter) if you play mesmer: You MUST shatter.
You shatter your clones if you are sure that can summon clones afterwards (2 at the very least, 1 more coming from a phantasm). Other than I would make sure to first use your dodges before you sacrifice your clones.
The only time I would shatter without making sure that you can resummon is when you need to do some breakbar damages, so if you see the breakbar of any random mob close to be replenished, I would advise to keep the clones up, use your sword ambushes and then press the f3.
Depends on build. If you're running with Illusions traits then you should shatter. It's power damage + torment.
If you're not running with Illusions trait (but chaos instead), then you should at least shatter F2 for confusion.
Master of garbage builds and being useless.
Shatter when you can instantly regenerate 3. If you just F2 shatter on cooldown that will be more than enough to do any pve content, but if you want to max dps you need to learn to use all shatters & double shatter. F2 then F1 priority.
According to Snow Crows:
The optimal time to shatter is when you can instantly get 3 Clones back up afterwards.
In addition, it's noted that it's most beneficial to do so, while you have a Phantom currently active, as it will become a clone when it finishes attacking.
An example rotation would be something like:
To be honest, this style of play where you keep 3 clones up at all times works well for any Mesmer build, condi, power or boon share. Since it capitalizes on the flexibility available to you, since maintaining 3 clones means you can decide which shatter is best to use at any given time as well as make use of F3 to damage breakbars when necessary (As not all bosses have breakable bars 100% of the time, some only activate during specific attacks)
As well as the passive benefits from clone attacks (Sword strips boons and stacks vulnerability, scepter/axe/staff applies condis, if Mirage then GS stacks vulnerability with Infinite Horizon)
Also, for open world, sometimes clones soak some attacks from bosses, keeping you and anyone you're doing events alongside, alive because no-one gets pounded into the dirt by some cheese massive boss hit xD