I've actually seen many cases where overuse of concrete types (on function parameters) in Julia can lead to poor performance. For example, if functions are written declaring an argument as `Vector{Int64}`, and then people using the function end up calling `collect` (and causing a lot of memory allocations), when they had a value that was an iterator and were forced to convert it into a vector just to call the function. Simply leaving off the `::Vector{Int64}` and getting rid of the `collect` on the caller speeds things up nicely.