General questions on ethernet communication between Siemens PLC's

When settion up ethernetcommunication between two S7 300 plc's you can choose to use an S7-connection and use the communication blocks FB12 "BSend", FB13 "BReceive", FB14 "Get" FB15 "Put", FB9 "URCV", FB8 "USND". Another way is to set up a TCP or Iso on Tcp connection and use FC5 "AG-Send" and FC6 "AG-Receive".

What reasons could there be to choose an S7 connection to a TCP connection?
Why not always a TCP-connection?

I thought that the CP343-1 Lean could have no S7 connection itself?

How about the data consistency at the receive side, can I be sure large datablocks are consistent
if using FB 13, FC6?

What if I use a put-function in the sender, can I be sure then of consistent datablocks at the receive side (because the receiver does not acknowledge I think??)?

What about consistency at the sender side? If I start the communciation function to send can I change data in the send block immediately after send start, and be sure that with this send task only the data from just before start of the send function is sent?

What are the data volumes that can be sent with the different communciation functions, connections?

Thanks