Algolia 1.6.1 or higher comes with a new feature that automatically updates your product index, every time you save a category. The disadvantage is that it will also update the product index, even if you just change an attribute which has nothing to do with URL rewrites or something else that can break search results. This can increase your indexing operations rapidly, therefore your monthly bills from Algolia as well.
To prevent unnecessary indexing, you should disable the new feature in System > Configuration > Algolia Search 1.x > Advanced > Update product on category products update and manage indexing manually with System > Index Management or simply with cron jobs.