Pets use the same navmesh method regular sims do and thus, they take up a household slot. You could look at household slots as navmesh slots actually. This is why the more Sims you have, the slower the game is (more noticeable if you have large houses with multiple floors and even, with cheats, increased the household size). Sims in The Sims 4 have to recalculate their navmesh before every action they take and they all have to do it separately (most likely a byproduct of the fact the game was meant to be an online game). A square room with a bookshelf in the middle might need to be divided into anywhere from 8-20 depending on many things (size of the bookshelf, wether the navmesh takes into account which side the bookshelf the sims can use it from ect. An empty, square room can be easily divided into 2 large triangles. If you place a bookshelf in the exact middle of the room, then the code responsible for calculating checks how many triangles will it need to divide the room into. Just to give a simple example: navmeshes usually work with triangles. Navmeshes are easy to calculate on a simple and small lot but it gets very expensive from a computational perspective the more stuff there is. Navmeshes are used to determine if a sim can move to a certain location and what route they need to take.

Previous Sims games usually had precalculated navmeshes. It's an unfortunate byproduct of how the game is made. I also miss training horses for competition, that was brilliant. My all-time fav were tiny cat families on houseboats! I would have a diver sim live on a houseboat with a bunch of cats, sometimes even make them a mermaid for fun and have a blast with the cats. I loved interacting pets with pets the same way I love sims with sims. I loved that despite them not being that playable, you could do smt w them. I loved taking babies outside, attending events with them, visiting families w babies to 'show off' Etc. There was a ,Going crazy' Moodlet in Sims 3 that showed up when you were inside your house a lot, which would def appear if you had a baby in the Sims 4 Object form. I get that interacting with complete babies is stupid, but I loved when I could take them outside on a walk.

Why? Becauss not controlling them makes sense only if you play as one sim in your household.

T H E M E B Y R O X I E PIXEL UNION | Extended photoset

Sims 4 controllable pets mod