host statement...

[Eustace, Glen]

> The first statement gives a hostname to a particular MAC

Yes,. But it also puts it in the class of 'known clients'.  Our policy is not to give leases to unknown clients.

> The second statement gives the fixed address to the hostname

Yes, but only if it is trying to boot in the subnet 10.123.255/24, anywhere else on the network and the first definition is used and a pool address allocated.