Warm up is according to what will happen after.
For a class for example, I give certain warmup as the subject of the class.
Ofcourse there is a general warm-up everytime, with breathing, stretching, fast warmup (cardio), etc.
For a performance a short 5 min warm-up is at least necessery. If the dancer is gonna do something extra-ordinary (like a deep back bend) its NEEDED a very good warm-up of the spine etc.
Advice, never ever dance without a warmup, for class or performance.
In class, I always make the same warm-up with my students, alwyas on the same music, it's like a ritual.
I make a quick part, which is choreographed, where the arms, the shoulders, the coordination and the ankles are trained.
Then, I warm up on the floor
-torso and hips
-back of the tigh
-front of the thigh
Before a performance I try to mobilise the same muscles, without rolling on the floor...
Class warm ups are head to toe.
For me as a performer, even in the SMALLEST of backstage areas, I will do a full back stretch, front and back thigh, neck and warm up my rotator cuffs (in the shoulders). If I have a (sigh) dressing room, I do a more lengthy warm up and hit all the areas where I'll need the greatest range of motion, like my hip flexors etc.
BTW...I also do a full warm up at home before leaving if time permits...I find that when I'm due to dance somewhere where they have no time or room for warm-ups, the pre-warm up really helps!
I do a cardio warm up that lasts 10 minutes. It begins at a gentle speed and gradually increases in intensity as each minute passes. I do a pulse in place, lifting the heels off the floor alternately, an undulating walk, walk in releve, a saidi step that I travel with, quick step together step, grape vine, shimmy, fast walk in releve, and a pulse in place double time... Before performance I do some ballistic stretches after I warm up.