Is Galera Arbitrator really required? I have three nodes(as recommended, in different switches) forming a Galera Cluster. Is there any real requirement of 'Garbd'? I don't see much reasons for using this apart from avoiding split-brain or taking backups?

Another doubt regarding garbd is that suppose I have 3 nodes in the cluster, and adding a garbd node will make the cluster size of 4, which is an even-numbered quorum. Will this not cause a split-brain situation?
If you have minimum of three active nodes in your cluster, you don't need to add garbd.

You should use a garbd with the following conditions:


When you have an even number of nodes and you can't add new nodes (because of cost or ...) to avoid split-brain situations. 
when you want to backup data (SST method) to a server.


More information:
http://galeracluster.com/documentation-webpages/arbitrator.html