What exactly is the meaning of "Subnet" parameter in tinc/$NETNAME/hosts/$SOMEHOSTNAME?

[Philip Blagoveschensky]

Hello, I am not very good at linux networking. I have read tinc documentation
multiple times and I still don't understand what the "Subnet = ..." directive
does in /etc/tinc/$NET_NAME/hosts/$HOST_NAME

Right now I have a simple virtual lan organized with tinc, and I use the
following in every device's config file (replacing the last part of the
address):

# This computer will have this ip address in the vpn
Subnet = 10.20.30.22/32

This allows me to connect to $HOST_NAME using ip address 10.20.30.22.

Now what I don't understand is why the guides on how to use one of tinc peer as
the default gateway tell me to write this too:

Subnet = 0.0.0.0/0

I don't understand what this does.
Why is it not enough to set routes on the client device like this?

ip route add 0.0.0.0/0 via 10.20.30.22 dev $NET_NAME metric 40
ip route add $SERVER_IP_ON_INTERNET/32 via 192.168.0.1 dev enp3s0

Does all this mean, that it's impossible to sometimes use $HOST_NAME_1 as the
default gateway and sometimes another $HOST_NAME_2, because their
`Subnet = 0.0.0.0/0` will clash, and something will fuck up?

-- 
Philip Blagoveschensky
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