In some cases when we are building dynamic expressions, it is possible to end up using multiple projections, for example:

queryable.Select(i => new { A = i.Age }).Select(i => new { B = i.A})

Applying SelectSelectCombiningTransformer make this LINQ to be combined and end up in NotSupportedException.

I removed the transformer and there was no side effects, just two of tests were failed which excepted the exact query. 

Here are name of the tests:

Largest_and_smallest_cities_by_state
Largest_and_smallest_cities_by_state_queryable_syntax

If we could make usage of this transformer optional, it will cover more situations.