What does BNLS_ReserveServerSlots do.. exactly in simpler English.
[code]
BNLS_RESERVESERVERSLOTS (0x12)
------------------------------

This message reserves a number of slots for concurrent NLS checking operations.
No other NLS checking messages can be sent before this message has been sent.
This message cannot be sent more than once per connection.

(DWORD) Number of slots to reserve.

BNLS may limit the number of slots to a reasonable value.



Response:
---------

(DWORD) Number of slots reserved.

This may be equal to the number of slots requested, although it does not necessarily have to be the same value.
Valid slot indicies are in the range of [0, Number of slots reserved - 1].
Each slot stores state information about a NLS checking operation.
A logon checking session must be finished on the same slot on which it was started.
If a logon checking session is abandoned before it is completed, no special action is required. Starting a new logon checking session on a slot overwrites all previous state information.
A logon checking session cannot be resumed if the connection to BNLS is interrupted before it is completed.
[/code]


What are slots?

I would imagine it's used when you are running a Bnet-like server, so as to allow you to check multiple user's hashes, etc, concurrently.