Local and global indexes

[Sumit Nigam]

Hi,
I had some doubt about local vs global indexes in Phoenix. 
In my use case, I have both read and write heavy use cases against the same 
tables. So, is it a better idea to use local indexes?It is also going to help 
reduce network chatter. 
Plus, my reads may issue queries which fetch non-indexed columns as well.
Should I keep both global and local indexes on the same secondary index column?
Thanks,Sumit