It’s not good practice. Really one shouldn’t be assuming anything is private or some entitlement to privacy on a service where all content you post is made publicly available to any and all linked instances. They miss the point of a federated public forum. If one wants privacy, data must be kept locally only. That’s why Lemmy has local-only communities, the “private” community aspect that many people want just won’t be federated, because you can’t make something like this private otherwise.