Set default jQuery version to at least 1.7 which is safe option for most of sites, newer is better.
Override default jQuery version for your admin theme - set 1.5 or even 1.4 (shipped with Drupal core). With newer versions issues in admin UI are possible.
Provides a registry for meta-data about Drupal variables and some extended Variable API and administration interface.
Other modules can know about your module's variables and they can be translated, exported, used in views, etc.
You'll get automatic variable edit forms, tokens, access control and uninstall for free.
Your module's variables will be allowed for Variable Realms being able to get values for each language (Internationalization) or Domain (Variable Domain).
Sometimes you'll have it just as dependency for other modules.