Serverless why and why not?

Usecases

Asynchronous, concurrent, infrequent, in sporadic demand, unpredictable variance in scaling requirements, stateless, ephemeral, and highly dynamic

Examples: Image/video processing, CICD, event streaming

You are free from: server provisioning, maintenance, updates, scaling and capacity planning

There is a lack of standardization and interoperability between cloud providers that may lead to vendor lock-in – CNCF
Aniszczyk explained serverless is not a good option for users that are looking at startup time and performance or trying to avoid being locked into a specific cloud platform provider.
Long running work loads
If you need advanced monitoring
Latency due to cold start [Download code, Start container, Bootstrap the runtime], then hot start [Start your code]