Separating the calf does have its advantages.
You will know if the calf is consuming milk or not.
You will know when the cows udder is completely milked out or not.
The cow will let down her milk for you rather than holding it back to feed her calf.
Because you are milking her twice a day (at least) you will see very quickly if her udder is injured or if she has mastitis.
As the calf gets bigger it consumes more and more of the milk.
They do not 'need' all the milk a Jersey cow will provide,
the milk could perhaps be used to better advantage in your milk bucket.
A calf can be hard on that udder.
They pick their 'favorite' quarter or 2 quarters and nurse only those if they have the option.
They hammer the udder with their hard heads and they have sharp bottom teeth that can do damage too.
I know their are those who successfully share milk with calves and I will let them tell you about how that works for them.
I don't personally recommend it, from my own experiences.