> im really missing concept of any cloud/online password manager ... im just curious of benefits and hope to get enlighted by people who use it.

Since you are curious, here are two reasons:

1) I regularly use multiple devices, and it is convenient. For example, lately local business require online orders/reservations. If you set up an account up using your laptop, then you can immediately login to the account on your phone.

2) I trust the math behind online password managers. For example, see this white paper describing 1password https://1passwordstatic.com/files/security/1password-white-p... In particular, see pages 10-11 (two-secret key derivation 2skd) and page 18 (How Vault Items Are Secured). As long as the 2skd protocol is implemented correctly, then it should not matter if the password manager is hacked. Presumably the few dollars a month you pay for the service is used to pay someone to carefully check this code.

Edit: In theory 2) reduces the "attack surface" to just the code implementing the 2skd protocol