It happens we do not move our appliances to clean behind them. Only moving them when they fail or we decide we want an upgrade.
The problem with that is many times they provide the right conditions for mold to grow. Unchecked for months at a time. Resulting in a surprise.
Refrigerators are prime suspects often in a corner. Especially new ones that have water and ice systems. A small break in a line or a slow leak that does not affect the overall function.
When the equipment is moved or replaced you can be left with a nasty mess. Many times the floor can be compromised depending on the conditions.
We recommend moving your appliances quarterly as part of your deep clean process