It will load balance the requests between the nodes configured in the hosts setting of the elasticsearch output.
Only if you configure just one node, but if this node is offline for some reason, it can lead to data loss.
Also, the node you configure in the output of Logstash is the node to where Logstash will send the index request, this does not mean that the data will be written to this node, Elasticsearch can choose to write the data on other node for example since it will balance the shards evenly between the nodes in the cluster.