A dimensionist's standout trait is their ability to spawn more allies, prioritising quantity over quality. While their summons are nowhere near as durable or powerful as a character of the 5 other classes, they are completely expendable.This class is particularly fragile due to a lack of defensive abilities. Since their armor does not provide a lot of protection, they will be relying on their allies (summoned or otherwise) to take hits for them, while they stay in the background strategizing and augmenting their allies' abilities.
Since dimensionists do not have any means of attacking, turns not spent summoning should involve using the class's extensive repertoire of buff and effect spells. These enchantments can be used on any of your allies, so don't hold off on enhancing your personal army just because they are expendable.
A dimensionist can also be treated as a healer. If you have a few more summons out than you really need, you can sacrifice one of them and give their health to another ally. Once again, this health can be given to both humans and other summons.