But perhaps most relevant is that a Great Deed could be used to gain permission to open an official Branch of the Colleges of Magic.
The most prominent example is probably the Hochland College of Sorcery, but other examples are the Wizards and Alchemists Guild of the Gold College in Middenheim, the not-actually-ancient-by-any-measure Ancient Library of the Light College in Tubingen, and the Esoterica Wing of the Royal Academy of Talabecland partnered with the Jade and Amber Colleges. They can serve many purposes, from libraries to research institutes to educational facilities to bases of operations. One obvious benefit is that a Wizard operating as the head of an official branch of the Colleges of Magic is an individual that gets treated with more care and respect than a lone Wizard operating as no more than themself. Another benefit is it makes the headquarters of your branch officially part of the Colleges of Magic, giving them various esoteric legal protections, a modest payroll, the option to bring in Senior Apprentices and Perpetuals as staff, and making it possible for them to attract investment from interested parties, such as College leadership or local rulers.