Ex. It is when he is talking about his immediate and extended family that he comes closest to taking responsibility for “doing” rather than letting things happen.
Q. I would like to understand the grammatical construction of the sentence. The that clause is tied to "it is"? Much like "It is so obvious that he didn't put time into it"?
So don't use it unless you have a reason to (to add emphasis, say). A lot of people just use it automatically, for the dubious fun of adding syntax and complexity and verbiage.