Magento 2 blocks and templates

Following are the 4 conditions.

  1. Single block and multiple templates – I think this is possible and we use it frequently while customizing Magento.
  2. Multiple blocks and single template – Never seen this one though.

Also not sure about below conditions too.

  1. Multiple block instances and single template
  2. Multiple block instances and multiple templates

Can anyone explain the above conditions and deduct whether these are true or not?