Each NTJ type seems to do a lot of both, though there seem to be extremes on the E/I ends. ENTJs in general seem more into the 'practice', whereas INTJs seem more into the 'theory'. But obviously, they all like to use practice and theory together, even if one is preferred. However, there seem to be little exceptions here and there, where they will both very strongly either be pragmatists or theoreticians (which I will outline).
The case for 'Pragmatism':
1. Many NTJ atheists (and there seem to be a lot of them) don't believe anything without evidence or experimental proof (like the existence of God).
2. Even if God or whatever were true, some NTJs would still would find exploring this topic useless (unless it gives results in a working procedure).
3. They want useful predictions for all processes and will only implement (in their blueprints for the future) productions that can be controlled.
The case for 'Theoreticism':
1. NTJ thinkers and sages can have a hyper-focused mental connection (like when they meditate) to a world that's very metaphysical in nature.
2. The 'systems-builders' will refine completely unprecedented revolutions in understanding the architecture of everything and what can be altered.
3. NTJ visionaries have powerfully prophetic or perhaps even 'psychic' revelations into a destiny that (within the intuitive 'flow' of events) is immanent.
I'm adding a poll in this thread (for NTJs) on whether they prefer practice or theory. Also, I could be wrong in parts of my above analysis on the NTJ philosophies, so I can be corrected.