Running functions in a VPC cause them to have cold starts of ~5 seconds. Connection pools need to be centralized to be of any use, since lambdas scale automatically.
I found myself in the middle of migrating a startup's entire "something" ingestion pipeline to be entirely done on Lambdas. For our purposes of one data block per every 10-20 minutes, and then processing and ingesting that data, Lambdas work perfectly, and about 10x cheaper than using ECS or EC2.