When I joined lemmy, I had to join a few different instances before I realized that:
Some instances didn't allow you to create new communities
Some instances were setup with an allowlist so that you couldn't subscribe/participate with communities on (most) other instances
Some instances disabled important features like downvotes
Some instances have profanity filters or don't allow NSFW content
I couldn't find an easy way to see how each instance was configured, so I used lemmy-stats-crawler and GitHub actions to discover all the Lemmy Instances, query their API, and dump the information into a data table for quick at-a-glance comparison.
I hope this helps others with a smooth migration to lemmy. Enjoy :)