Why doesn’t Gandalf use his power??

I dislike Allegory – the conscious and intentional allegory – yet any attempt to explain the purport of myth or fairytale must use allegorical language. (And, ofcourse, the more ‘life’ a story has the more readily will it be susceptible of allegorical interpretations: while the better a deliberate allegory is made the more nearly will it be acceptable just as a story.) Anyway all this stuff* is mainly concerned with Fall, Mortality, and the Machine. With Fall inevitably, and that motive occurs in several modes. With Mortality, especially as it affects art and the creative (or as I should say, sub-creative) desire which seems to have no biological function, and to be apart from the satisfactions of plain ordinary biological life, with which, in our world, it is indeed usually at strife. This desire is at once wedded to a passionate love of the real primary world, and hence filled with the sense of mortality, and yet unsatisfied by it. It has various opportunities of ‘Fall’. It may become possessive, clinging to the things made as its own, the sub-creator wishes to be the Lord and God of his private creation. He will rebel against the laws of the Creator – especially against mortality. Both of these (alone or together) will lead to the desire for Power, for making the will more quickly effective, – and so to the Machine (or Magic). By the last I intend all use of external plans or devices (apparatus) instead of developments of the inherent inner powers or talents – or even the use of these talents with the corrupted motive of dominating: bulldozing the real world, or coercing other wills. The Machine is our more obvious modern form though more closely related to Magic than is usually recognised.

I have not used ‘magic’ consistently, and indeed the Elven-queen Galadriel is obliged to remonstrate with the Hobbits on their confused use of the word both for the devices and operations of the Enemy, and for those of the Elves. I have not, because there is not a word for the latter (since all human stories have suffered the same confusion). But the Elves are there (in my tales) to demonstrate the difference. Their ‘magic’ is Art, delivered from many of its human limitations: more effortless, more quick, more complete (product, and vision in unflawed correspondence). And its object is Art not Power, sub-creation not domination and tyrannous reforming of Creation. The ‘Elves’ are 'immortal’, at least as far as this world goes: and hence are concerned rather with the griefs and burdens of deathlessness in time and change, than with death. The Enemy in successive forms is always ‘naturally’ concerned with sheer Domination, and so the Lord of magic and machines; but the problem: that this frightful evil can and does arise from an apparently good root, the desire to benefit the world and others – speedily and according to the benefactors own plans – is a recurrent motive.

He uses minor magic like flames to scare wolfs, and lighting up his staff. But anything really offensive seems to take a lot of energy, e,g he literally dies of what could be described as exhaustion in the fight with the Balrog, where he uses magic exclusively in the fight (off screen). Use of magic in the books is usually described as taking a lot of effort, physical and mental.

So scaring off wolves and making fireworks is virtually no effort, but fighting an equal 1v1 is going to be costly for both, and probably destroy a good amount of surrounding countryside. IIRC in the book Gandalf virtually dropped a mountain on the Balrog.

The witch king stand off is incorrect in the film, in the books Gandalf was winding up to use his full power against WK, but the WK found a good distraction to get him out of it. There was no staff breaking etc. In theory Gandalf would have nuked the WK but that would have left him considerably weakened with more equally powerful foes to face.

So people don't use powerful magic directly as a weapon in LotR because of the risks in using it, the recovery time and the massive collateral damage.