TL;DR I would be happy if someone could write a guideline on how to handle the decision whether to give an app Network and/or Sensor Permissions.
From a privacy perspective, the network guideline could be summarized into one sentence, "Grant network permissions only to apps that you entrust with the personal information they will have access to."
Having network permission means that whatever information is accessible to the app can be sent home. That includes any information you provide the app directly, as well as any information the app has permission to access on your filesystem, and any information the app may obtain mutually from other apps via inter-process communication (IPC).
In my opinion, every app with network permission is essentially a backdoor to your device (within the confines of the app's sandbox) and any information the app can access. It can dial home, it can transfer data to/from your device, it can log your public IP, etc. My best advice is to think carefully about which apps are granted network access, particularly if privacy is a concern.