[SR-Users] rtpproxy module flags 1 and 2 question

i'm new to rtpproxy (have been using mediaproxy for years) and now try to understand if it would make sense to switch over. rtpproxy readme has this on flags value 1:

+ 1 - append first Via branch to Call-ID when sending command to rtpproxy. ... This is especially useful if you have serially forked call scenarios where rtpproxy gets an "update" command for a new branch, and then a "delete" command for the previous branch, which would otherwise delete the full call, breaking the subsequent "lookup" for the new branch.

how it would be possible in SERIAL forked scenario to get anything for a new branch before previous branch has first failed and gone?

-- juha