you need to figure out IF a particular transaction is YOURS! ... that's what happens when TITAN is scanning ..
Isn't that the same thing which happens with UTXOs in bitcoin? The wallet scans for transactions for which it has the private key and sticks them in a table somewhere?
In Bitcoin you derive the addresses for which your hold the private key and just
look for transactions that deposit into one of those addresses
with TITAN, the addresses are computed from the public key of the registered
account and the instructions to regenerate the private key that allows access to
the funds is stored in the memo. That's what happens in stealth addresses in
Bitcoin too ..
Hence, the BTS/stealth wallet has to scan every memo to figure out if it can
decode the data in the memo and find "instructions" on how to derive the private
key for the deposit