Much has been said in this thread about the Si-Dom's ability to store and retrieve facts, and that's undoubtedly a key part of what they do. But less has been said about what exactly they do with those facts: They generate rules.
To compare Si to Se:
Se operates on an ad-hoc basis, coming up with real-time interactive tools for real-time problems. Si, on the other hand, takes problems down into an internal laboratory and works out tools for a given specific problem as well as a number of related problems, i.e., it works out a personal *rule-based system* for handling a broad array of similar problems. In that respect, Si works out a kind of internal "delta" of Se. That is, it tracks lots of Se possibilities and works out an internal, personalized Si system for handling them.
Or in more practical terms:
Si intercepts, stores, and categorizes lots of data. Then it compares the data to each other to determine "best practices" for doing things, determine progress in things (change over time), etc. From that, Si can then generate rules and "automate" lots of daily routines for the sake of increased productivity: Where is the best place to buy furniture, what is the quickest way to put on make-up in the morning, what is the best way to balance their checkbook, etc. (I was married to an ISTJ for 10 years, and she was one of the most productive people I've ever known.)
It's this rule-making function that makes Si-Doms and Si-Auxes good at such jobs as the military, police, etc.: They love the standardization and automation of procedures for greater productivity, resulting in a natural affinity for environments that favor rules.
I posted a similar analysis about Ne vs. Ni in this thread:
http://www.typologycentral.com/foru...9182&page=60&p=2265546&viewfull=1#post2265546
With regard to Ne vs. Ni, I said, "Ne is ad hoc and operates out in the world; whereas Ni takes things down into an internal laboratory and tries to extract the *principles* that motivate or connect together related issues or events in the outer world."
Similarly, Se is ad hoc and operates out in the world; whereas Si takes things down into an internal laboratory and tries to extract the *rules* that motivate or connect together related issues or events in the outer world.
By the same token, Si-Inferior (shared by ENFPs and ENTPs) isn't just obliviousness to details; it's also a lack of trust in rule-based systems, automation, and repetitiveness. Hence, Ne-Doms (who share Si-Inferior) tend to want to do everything ad-hoc and fresh every time, as opposed to automating things; they hate routine because routine is repetitive and demands the generation of rule-based systems for proper mastery.