What is the requirement of label configs apart from it saves from purging. I need some elaborate explanations. Is it a template.
There are no requirements per se. The requirements are those YOU set out. Typically, customers label configs that are well-tested and audited. These can be baselines on which other changes can be made. For example, say you spend time going line-by-line through a config to make sure it contain no extraneous information, meets all your protocol and feature requirements, and contains no known bugs. You may want to label that config as "Production_Audited_20090809". This config would then be persisted in the archive even across purges. You can also do comparisons between this config and any later versions that may be created based on it (e.g. you make some changes at a later date, then notice some unexpected behavior).
Put simply, labels are just logical ways of naming certain configurations.