The following quote from Anthony Burgess has a comma after it:
There is, in fact, not much point in writing a novel unless you can show the possibility of moral transformation, or an increase in wisdom, operating in your chief character or characters.
But this quote from William S. Burroughs doesn't:
There is in fact something obscene and sinister about photography, a desire to imprison, to incorporate, a sexual intensity of pursuit.
When should you use a comma after "there is in fact"?
Is it necessary to put a comma after "there is in fact"?