Let me add: version 3.0.0 was very small and simple it didn't have a full notion of index management. More modern versions are able to share a single index for multiple types without problems, they'll share the writer and index scoped settings and you'll see writes are way more efficient than what they used to be as we do smart things with write buffers.

The only case to worry about exclusive_index_use is when you have multiple instances of Hibernate Search sharing the index, as in this case they can't be smart about sharing those resources and need to aggressively close all buffers after each write and release the write locks. It's enabled by default now as there is no much practical need of ever doing this, a single instance is much more efficient.