Couchbase tutorial and multiple bucket

Why in most couchbase tutorials we have more that 1 bucket?
for instance

AFAIK , just one bucket is enough for most applications and if you can create an application using 1 bucket it is highly recommended do that instead on using multiple bucket

You are correct that we recommend using fewer buckets to reduce overhead.

I suspect that the documentation uses multiple buckets to make the concepts easier to understand, since many people are coming from the relational world with multiple tables.