The idea is that since ranges have O(1) reductions such as minimum, maximum and sum defined, we may reuse the implementations in the corresponding reductions with init specified, instead of hitting slow fallback implementations.

for example, after this,

julia> @btime maximum($(Ref(1:10000))[], init=typemin(Int))
  2.344 ns (0 allocations: 0 bytes)
10000

whereas, on master, this is O(N) as it loops over each element.

The specific use case is to avoid hitting slow fallbacks in a change like https://github.com/JuliaLinearAlgebra/BlockBandedMatrices.jl/pull/218/files.