Lazy indexing used to be an option. It’s not in any CosmosDB documentation anymore. By using Lazy indexing, you could save 20 to 30 percent for Request Units. Just like anything else in life, you get what you pay for when it comes to Lazy indexing. By selecting Lazy indexing, you are saying that eventually Indexes will be updated. If Indexes are not updated, that means your queries might not return all the data since all data might not be indexed yet. Lazy indexing is still an option, nobody talks about it for a good reason. In my opinion, it should be listed as obsolete feature or it should have a better documentation about how it works or why it might not be a good option for your solutions.
If you use Lazy Indexing to reduce Request Units in your solution, change it to consistent now unless you have a really good reason!
Read on for more advice in this vein.