I only use owner profile. But I would like to point out from observation here that users of multiple profiles experience way more buggy behaviour and certain not so benign cross profile data leaks (which may be upstream AOSP bugs, but bugs nonetheless, often unadressed). Ragarding IPC, I consider existence of Play Services and Framework on your device the main issue related to potential inter app communication since it is the most common compatibility link. I refrain from using it because of its network reliance and permission invasiveness, regardless of the fact that it is sandboxed. Most of my online services are accessed via Vanadium only, which greatly reduces attack surface not having to otherwise rely on many additional native apps.