Hash index for sid?

Question

MongoDB

Hello
Using a module like this for persistent storage of sids, what are the pitfalls by changing the index type of the _id field (where the sid is stored) from B-tree to Hash ?
I see only a problem with a delay when rebuilding the table ( hash = data mod x - changing the number x with an increase in the amount of data (if the module was used as a hash function :) ) )
And the tree for sids is a rather useless thing, since no one is going to sort it or write range queries