Different people want different things
The people who want to see photos of your dog aren't necessarily the people who want to see updates about your kids. The friend you'd send old horror movie recommendations to might not care about your summer garden. We have many different "audiences", and they don't always overlap.
Most sharing tools give you one audience. On Facebook and Instagram it's your followers or your friends. Instagram has Close Friends, but it's just one list. Usually you don't get much control beyond sharing everything with everyone, or not sharing it at all. That has a big impact on what we share. When it has to work for everyone who follows us in an app, we end up sharing less, or sharing more polished, safer versions of things. You're sharing for the wider group, and you almost forget that you're sharing with a bunch of individual people.
In a Pool, the audience belongs to the subject. You decide what it's for and who's invited when you create it. So you might have one Pool for the dog, one for the kids, one for the garden and one for horror movies. Your grandmother is in the kids Pool and probably not the horror one.
That removes a decision, because once you've got the Pool, you already know who's the audience for that Pool. A dozen garden photos might feel like oversharing on social media, but they're exactly what the few friends in your garden Pool want to see.
Plus, the people you invite from different parts of your life don't need to know each other. If your grandmother and a friend who has never met her both follow the same Pool, they don't see each other as members unless they're already connected. That works because Pools is built on Bonafide, where each person has their own database and connects with others one at a time. Who can see whom follows from the connections people have made.
The same idea applies to conversations. A comment on a post usually goes to everyone who can see the post. In a Pool, whoever starts a comment thread chooses who's in it. Say you post a photo and your sister has something to say about it to your partner. She can start a thread with your partner and leave you out. A dinner table works like this, with the main conversation and the side ones, and most online tools flatten them into one thread that everyone can read.
None of this replaces the group chat. It's still the place for making plans and for conversation that needs a quick answer. A Pool is for the things people might want to follow over time, and for the things you'd share a lot more of if you knew it was only going to the right people. It's not oversharing when it's for the people who actually want to see it.