OK, I'll try to explain this case in details.
Imagine that you are creating new mosaic. Name it, i don't know, VirtualUSD (divisibility 0, total 1 000 000). To make it transferable we should send some XEMs in transactions alongside with our VUSD. Otherwise, end users will receive only VUSDs. They can not transfer it further because each transaction implies at least 2 XEM fee.
OK, we can make our newly created mosaic trully transferable if we include enough funds for the endpoint users to pay the fee. So, we need to add 200 XEMs to transfer 100 VUSDs in order to allow our recipient to make up to 100 further transactions with 1 VUSD each. But all 200 XEMs will be spent on these transactions. Therefore, again, the 2-tier recipients will not be able to transfer funds further because they will receive only 1 VUSD each and no XEMs at all.
We can add some levy to balance transactions. In our case if we set levy amount to 1 VUSD all the fees will be compensated.
1. Main account sends 100VUSDs to user1 (user1 will receive 100 VUSDs + 200 XEMs).
2. user1 sends 99VUSD to user2 (user2 will receive 99 VUSDs + 198XEMs), 2 XEMs fee and 1 VUSD levy will be subtracted from the user1's account, total balance will be 0 VUSDs (and 0 XEMs).
3. user2 sends 10VUSD to user3 (user3 will receive 10 VUSDs + 20XEMs), 2 XEMs fee and 1 VUSD levy will be subtracted from the user2's account, total balance will be 88 VUSDs (and 176 XEMs).
It looks like the easiest and the most natural way to organize transfers from the scratch. In this case wallet for our VUSDs can be easily implemented.