I understand the general notion in play: if my laptop/computer is stolen or compromised I can revoke that particular subkey so (as long as people have updated their keys) they can't impersonate me. However, the compromiser can still read messages intended for me as far as I understand. So, maybe I don't lose signatures but if the thief has a way of intercepting messages intended for me (and if they have my laptop they very well might), they would be able to read them. Am I misunderstanding or is the creation of subkeys lest beneficial than some make it out to be?
The usage of subkeys separates the collection of trust signatures from the key's usage. Trust signatures for the Web of Trust are created for you master key. This trust is inherited by your subkeys which are the ones used in the actual cryptographic operations (signing/decrypting). This has a few advantages:
- Key rollover: You can use short lived subkeys (usually 1 year) which can be updated regularily without you losing the trust signatures collected.
- Key compromise: As you stated, the master key should be stored offline to mitigate the consequences of a key compromise. If your subkeys are compromised, they can easily be revoked and replaced. Past communications will be left vulnerable but not future ones.