deltuzirtu If an ap in the main profile suits you with permissions that you can control, such as storage scope, sensors, etc., there is no reason to place it in a separate profile.
From a practical standpoint, placing an application in a separate profile/private space is useful when you need to use an application that you do not particularly like, for example for work or social media, and you want to be able to lock this space so that it does not run in the background or constantly appear in your list of applications. You could imagine two personas, one for personal use and one for work.
From a purely security standpoint, it's not really useful because all applications are strictly sandboxed, and mutual communication between multiple applications via IPC is not a security issue.
From a purely privacy standpoint, applications can communicate via IPC. For example, WhatsApp could communicate with Instagram because they both come from Meta. Whether this is acceptable or unacceptable in terms of privacy depends on you, your choices, your beliefs, etc. Some people do not accept it, and others do not care, and there are no right answers.