Use Cases and Deployment Scope
I have used Sendgrid since before Twilio purchased the business to send transactional emails to customers. We used it for welcome emails, password reset emails, MFA tokens, and general notifications. I've used Sendgrid in quite a few organizations - it's extremely easy to use and offers you the ability to connect through API or via SMTP, so it's really flexible.
Alternatives Considered
Amazon Simple Email Service
Other Software Used
Datadog, Planhat, HelloSign, Personio, Dropbox Business