I am a Growth Marketing Specialist working for startups and often use this tool with them basically because all the startups are B2B and SaaS.
Besides the other web and data analytics tools, this product analytics tool I use it to be able to identify what is the behaviour, events and paths the users take from specific utms campaigns. Amplitude allows growth marketers to track utms and we can easily identify in funnels the steps of the signup, onboarding or some user flows.
The thing that I most like about Amplitude is all the different analyses you can build and the easy way to choose events and metrics.
I was missing on this tool more integration with marketing channels but that is something that they have already implemented which is great.