Imagine the effects of summoning a creature you cannot wholly understand, but control. In fact, how much do you control this being? Imagine the horrour of bringing such a thing up only to have it follow its own agenda for a time. The games use them as slaves that simply vanish when the work is done... But what if upon besting its foe it is left to its own perversions until released. A foolhardy mage or one still new to such magicks could cause quite a bit of mayhem. That said, the mental challenge is probably just as true as for the summoner. Just how long can your sanity remain intact -- or does it chip away with each monstrosity borne by your hand?
Just imagine Constantine (television)'s White Castle.
That. . . is immensely interesting to think about. While I don't think it would effect Revral as much, given that he's been studying conjuration for over half a millenia, but it could be something to mess with if he's in a poor mental state. He lacks the will to control one of his summons, and it turns on the group. The possibilities are tempting, to ay the least. Also, I see possible confrontation between vampires, with the feeding potions being the source of it.
Not only what Pellegrino said, but I highly doubt people understand how hard it is to learn magic. In the game there are Mage Colleges and other institutions that teach people how to use magic. Whenever you're wandering around, you'll sometimes happen upon some poor fool who thought he could just pick up a tome and learn a new spell. Of course, by the time you happen upon them, they've already been burnt to a crisp because the spell backfired.
Casting spells, conjuration especially, taxes your mind heavily. This is why you see mages who've been practicing for years able to cast devastating spells. You'll see in the lorebooks that people are capable of summoning vampiric clouds to sap the enemy army's strength before battle, the Psijics were able to sink an entire Maormer fleet by conjuring up a storm and naval warfare is made extremely potent if the enemy crew has a mage.
The games portray them as slaves, which is true. Pellegrino conveys it very nicely. What you're actually doing is you're pretty much doing what the Jaeger pilots in Pacific Rim would do with each other, kind of. You're using your mind to create a bridge to push your thoughts into that creature's head to make him do what you want. Of course, this creature wasn't just summoned from a vacuum, he was taken from one of the innumerable planes of Oblivion and it is the conjurer's job to make sure his will overpowers the creature's lest the creature gets pissed that it isn't home anymore and kills every strange face around it. These creatures you're summoning are living things with their own lives, their own thoughts, their own feelings and they wouldn't appreciate being snatched away from their loved ones, let alone snatched away at all.
That being said, Revral would know his limits and know that there is a time and a place for pushing his limits and practicing, but the middle of a battle is not that time or place.
Edit: Boy, this post just keeps getting bigger, huh? I just want people to know that, just like the Wu-Tang, magic ain't nothin' to fuck wit'.
It's useful to think of it this way -
Somobro on Reddit's TESlore subreddit said:
This is more my own analogical take on it but I always thought of the use of magic to be akin to our use of experimental physics and chemistry. Sure, everyone can do it, but most have to follow a close set of instructions in order to reproduce difficult and complex experiments (or use scrolls to perform difficult spells without the appropriate skill). The remaining minority have the learning and knowledge to not only recreate experiments (perform spells) but also create their own reactions (create spells). To do the latter takes years of hard work, some semblance of natural intelligence and on top of all that a degree of aptitude to the art. Trying to do difficult experiments at home without proper tools and supervision will result in probable damage to yourself and your surroundings, which is the same for amateurs in nirn attempting to perform spells beyond their ability.
In the end, all our top scientists attend universities where they hone their craft with like-minded peers and well-practiced teachers. They almost always wind up writing books and papers, and some are feared by the ignorant public for their experiments and knowledge, which they feel threatens to go too far and destroy their world, just like in real life (I know a lot of people who are still vehemently anti-hadron collider because it'll create a black hole and kill us all).
tl;dr: Magic is like advanced science, everyone can technically do it but only the naturally intelligent and appropriately inclined attempt to practice it without getting bored or frustrated easily.
