It can be. The engine doesn't get up to operating temperature. That can cause some problems over time.
the engine needs run at its it's peak operating temperature for about 20 minutes at least once a month in order to burn up certain deposits that can affect performance and engine life.
yes
Legend has it that highway miles are better than short distance miles.
Especially in the winter. Combustion produces steam. If you never get the pipes hot, the steam condenses on them, into water. Water on steel causes rust.