If someone gets physical access to the phone, most data is certainly compromised. But there is still value in a passcode, as the system/apps on an iPhone can s

If someone gets physical access to the phone, most data is certainly compromised. But there is still value in a passcode, as the system/apps on an iPhone can store the most valuable data (e.g. saved passwords) encrypted using the passcode as the key. Without a passcode losing your phone means immediately losing the keys to your entire online kingdom. Especially if you have email credentials set up. (Even if you have been using a passcode when you lose your phone you should still change your credentials, but in the meantime it is much less likely that your accounts are compromised.)