Escrow and Lock Funds Transaction

Technical Discussion
#1

While following the tutorial on https://nemtech.github.io/guides/transaction.html#creating-an-escrow-with-aggregate-bonded-transaction, it mentions

“When an aggregate transaction is bonded, Alice will need to lock at least 10 XEM.”

As in the aggregate transaction the amount is 100 XEM, I want to ask if 10 XEM for locking is because of some rule? If so, is it based on the ratio (at least 10%) or absolute amount (at least 10 XEM no matter how much you have) ? And lastly, why not locking the whole amount needed for transfer?

#2

It’s so you can’t announce a bunch of aggregate tx that’ll never be co-signed i.e. to prevent spam. You could do that with a fee (as it’s basically now for multi-sig tx) but they chose to go a different route, which makes it’s somewhat less convenient but cheaper (i.e. you get the 10 XEM back).
There’s no reason to lock-up more XEM much less the entire amount. Unless you see one ?

#3

makes sense for spam prevention part

i was thinking there might be some cases that you may need to customize the amount that you are locking