Prior to Multi-Genre, you’ve likely been focusing on a few specific single-genres and probably have a team with skills that match those genres.
Multi genre opens the possibility for new genre combos and thus new ideal tech/design ratios. Hiring 2 new people gives you the opportunity to shift the tech/design balance of your company based on the skills of those who you hire. Combining the two allows you to shift your company and immediately making full use of multi-genre. Picking a multi-genre combo that maximizing slider flexibility is also key to being able to make Large games with just 5 people (before the 2nd office unlocks).
Multi-Genre also unlocks around about the time you have about 250k fans, the number needed to self-publish large games. If you have fewer than that, do some large publisher contracts until you do. This will set you up nicely to make Large games your norm, even before moving into the last office.