For longer tasks, spinning up an EC2 or Beanstalk instance is probably the way to go.
As for what to use it for, we used it in our application (deployed to Netlify which uses Lambda under the hood) where lambdas operated like a 'proxy' to various 3rd party API suppliers (Commercetools, Adyen, some age verification service), and those too would use a lambda function to ping back at us (e.g. when payment was confirmed). Worked pretty well, although in retrospect I would've preferred a 'normal', monolithic server to do the same thing.
For longer tasks, spinning up an EC2 or Beanstalk instance is probably the way to go.
As for what to use it for, we used it in our application (deployed to Netlify which uses Lambda under the hood) where lambdas operated like a 'proxy' to various 3rd party API suppliers (Commercetools, Adyen, some age verification service), and those too would use a lambda function to ping back at us (e.g. when payment was confirmed). Worked pretty well, although in retrospect I would've preferred a 'normal', monolithic server to do the same thing.