These are primarily intended to be used in Repositories. Repositories are experts at interacting with their associated storages. They should catch storage exceptions, interpret them (since a lot of storage exceptions have esoteric codes or, worse, esoteric message strings that need to be identified for certain cases) and decompose the specific storage exception to be either Transient (this will get better) or NonTransient (this needs a human, i.e. it will not get better.)

Example

//...
} catch (\Doctrine\DBAL\ConnectionException $connectionException) {
    throw (new TransientException())->setPrevious($pdoException);
}    
return $this;