Use of Serialization Version UID in Java

The purpose of the serialization version UID is to keep track of different versions of a class in order to perform valid serialization of objects.
The idea is to generate an ID that is unique to a certain version of an class, which is then changed when there are new details added to the class, such as a new field, which would affect the structure of the serialized object.
Always using the same ID, such as 1L means that in the future, if the class definition is changed which causes changes to the structure of the serialized object, there will be a good chance that problems when trying to deserialize an object.
If the ID is omitted, Java will actually calculate the ID for you based on fields of the object, but I believe it is an expensive process, so providing one manually will improve performance.