[IanCal]

I have several projects that use different versions of elasticsearch and different versions of postgres.

Elasicsearch has differences through versions which make some of the code incompatible (I recall changes with security around custom scoring functions). Some projects depended on an older version which allowed this code, other projects depended on newer features. Being able to have a different configuration per project can make things much simpler.

Even with the same versions, I'd like my ES process to be used by only one project, otherwise there's a risk of them stamping over each other causing issues which wouldn't be seen in production.