Use of master-eligible nodes that are not acting as master?

Elastic Stack Elasticsearch
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From the documentation:

Indexing and searching your data is CPU-, memory-, and I/O-intensive work which can put pressure on a node’s resources. To ensure that your master node is stable and not under pressure, it is a good idea in a bigger cluster to split the roles between dedicated master-eligible nodes and dedicated data nodes.

Our cluster currently consists of 13 nodes, where all nodes are data nodes and nodes 1-4 are master-eligible nodes. We're having performance issues so I'm thinking that maybe it's time to remove the data role from the master-eligible nodes (according to the quoted text above).

Question: If we have four master-eligible nodes that are not data nodes, what use will we have of the three master-eligible nodes that are not acting as the master? Will they add value to the cluster during this time or only be of value as fail-over if the current master goes down and a new master needs to be elected? Will they basically be idle all of the time when another node is acting as master?

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Although the extra master nodes won't necessarily be using all their resources at all times, that doesn't mean they are not valuable. There is a great deal of value in having enough redundancy in your systems to cope with inevitable outages.

Four master-eligible nodes are no more useful than three, however, because both configurations can tolerate the loss of just one master-eligible node. I would recommend sticking with three. You could also try having just two dedicated master-eligible nodes together with a voting-only master-eligible node which could reasonably be one of your data nodes.

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