Amazon Athena is the simplest way to give any employee the ability to run ad-hoc queries on data in Amazon S3. Athena is serverless, so there is no infrastructure to setup or manage, and you can start analyzing your data immediately.
If you have frequently accessed data, that needs to be stored in a consistent, highly structured format, then you should use a data warehouse like Amazon Redshift. This gives you the flexibility to store your structured, frequently accessed data in Amazon Redshift, and use Redshift Spectrum to extend your Amazon Redshift queries out to the entire universe of data in your Amazon S3 data lake. This gives you the freedom to store your data where you want, in the format you want, and have it available for processing when you need.