Disabling Require Locale means leverage will ignore the country code of the source and the target language when determining which TM unit to leverage to the segment rather than matching on the language and region code.
When you choose to disregard the region code, it will look for the highest, most recently created TM unit of matching languages.
As an example, a document translated from
English, United Kingdom into
Spanish, Spain may leverage an
English, United States - Spanish, Mexico if that TM unit was created sooner than another matching
English, United Kingdom - Spanish, Spain TM Unit.
This feature is excellent for companies who are looking to save on costs and are not necessarily concerned with localizing content based on region.
The targets listed here are the ones you set up in the Document Tab of the Setup phase.