Metric is an estimate of the 'cost' to deliver the traffic on that path.
It is only used if there appears to be a choice in alternatives.

The backgound on that is to understand the hierarching of choices in a route:

• the most specific route always wins
• a more specific is preferred over a general
• the default takes everything not resolved by a-or-b

a) the very specific would be a routing to one system; just like port forwarding is to one system; aa.bb.cc.dd with no wildcards
b) the more specific might be aa.bb.cc.0 with a mask of 255.255.255.250
(ie only 4 targets possible)
while a less specific migh be aa.bb.cc.dd with a mask of 255.255.255.0
(254 targets)

if the parochial software is not an impediment, then a very loose, yet specific route
might look like aa.0.0.0 & mask 255.0.0.0

and the default route (internally) would be 0.0.0.0 & a route of 0.0.0.0