I ask because my team previously was trying to "do" scrum. We had 2-week sprints, but no releases to go with those sprints! There were several other reasons for this, but one big one was that deployments took too long and were too complicated to do that frequently.
You sort of answered your own question: if deployments take too long, they can't be done frequently and you can't have short iterations, you can't ship the code at anytime, you can't demo progresses at the end of an iteration, etc. So, in your context, not having an automatic deployments was a major impediment that should have been identified and removed very early (through inspection and adaptation).
Back to the question now. Is automatic deployment a crucial practice? Well, as hinted, I'd say it depends on the context: a project with a simple and straightforward manual deployment process can probably live with it. Is automatic deployment a good practice? I think so: an automated process is typically faster, less error prone and humans obviously don't add much value at doing something that can be automated (see also Three Strikes And You Automate).