Why can't all zeros in the host portion of IP address be used for a host?

Posted by Grezzo on Server Fault See other posts from Server Fault or by Grezzo
Published on 2012-11-22T13:52:06Z Indexed on 2012/11/22 23:01 UTC
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netmask

I know that if I have a network 83.23.159.0/24 then I have 254 usable host IP addresses because:

83.23.159.0      (in binary: host portion all zeros) is the subnet address
83.23.159.1-254  are host addresses
83.23.159.255    (in binary: host portion all ones) is the broadcast address

I understand the use for a broadcast address, but I don't understand what the subnet address is ever used for. I can't see any reason that an IP packet's destination address would be set to the subnet address, so why does the subnet itself need an address if it is never going to be the endpoint for AN IP flow? To me it seems like a waste to not allow this address to be used as a host address.

To summarise, my questions are:

Is an IP packet's destination ever set to the subnet IP address?
If yes, in what cases and why?
If no, then why not free up that address for any host to use?

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