Elasticsearch solo vs Couchbase+Elasticsearch

Let me describe the issue. Now I'm at the stage of architectural
changes. I used to use Elasticsearch as aggregation and search tool, but
now I'm thinking about use it as main DB. I read that there is not
recommended to use Elasticsearch as a main DB, only as a index. So I
read presentation about connection it with Couchbase:

I downloaded and installed Couchbase and plugin for integration with Elasticsearch

I'm not convinced about this solution. Firstly, aggregation is faster
in Elasticsearch. Secondly, Elasticsearch supports histogram,
geopoints, full text search and many other, so it seems that only reason
to keep Couchbase is not to have Elasticsearch as the main DB.

So my question is about the benefits of integration Elasticsearch with Couchbase in my case?

You can have couchbase as the datastore, source of truth, and use elasticsearch for all the other things: aggs, search, get, whatever.

If your data are not sensible, like logs, then you can use elasticsearch only.
If not, you need to be able to reindex in any case. So keep your source of truth somewhere, filesystem, hdfs, database, couchbase... Wherever. In case of problem, you will be able to reindex.

Have a look also at this page: https://www.elastic.co/guide/en/elasticsearch/resiliency/current/index.html

Thank you for help. Now I know your answer was very helpful.