docs(feature-flags): add guidance when to use vs env vars vs parameters

Author: heitorlessa

Diff for: CHANGELOG.md

@@ -14,6 +14,7 @@ This project follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) fo
 * **deps:** bump poetry to latest ([#592](https://github.com/awslabs/aws-lambda-powertools-python/issues/592))
 * **feature-flags:** bug handling multiple conditions ([#599](https://github.com/awslabs/aws-lambda-powertools-python/issues/599))
 * **parser:** API Gateway WebSocket validation under check_message_id; plus some housekeeping ([#553](https://github.com/awslabs/aws-lambda-powertools-python/issues/553))
+* **feature-toggles:** correct cdk example ([#601](https://github.com/awslabs/aws-lambda-powertools-python/issues/601))
 
 ### Code Refactoring
 
@@ -30,6 +31,7 @@ This project follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) fo
 * **tracer:** update wording that it auto-disables on non-Lambda env
 * **feature-flags:** fix SAM infra, convert CDK to Python
 * **feature-flags:** fix sample feature name in evaluate method
+* **feature-flags:** add guidance when to use vs env vars vs parameters
 ### Features
 
 * **api-gateway:** add support for custom serializer ([#568](https://github.com/awslabs/aws-lambda-powertools-python/issues/568))

Diff for: docs/utilities/feature_flags.md

@@ -644,3 +644,11 @@ You can unit test your feature flags locally and independently without setting u
 		# THEN
 		assert flag == expected_value
     ```
+
+## Feature flags vs Parameters vs env vars
+
+Method | When to use | Requires new deployment on changes | Supported services
+------------------------------------------------- | --------------------------------------------------------------------------------- | ------------------------------------------------- | -------------------------------------------------
+**[Environment variables](https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars.html){target="_blank"}** | Simple configuration that will rarely if ever change, because changing it requires a Lambda function deployment. | Yes | Lambda
+**[Parameters utility](parameters.md)** | Access to secrets, or fetch parameters in different formats from AWS System Manager Parameter Store or Amazon DynamoDB. | No | Parameter Store, DynamoDB, Secrets Manager, AppConfig
+**Feature flags utility** | Rule engine to define when one or multiple features should be enabled depending on the input. | No | AppConfig