Avoid Copies of Arrays in MEX Functions

My question is about following example which can be found in documentation:

#include "mex.hpp"
#include "mexAdapter.hpp"

using namespace matlab::data;
using matlab::mex::ArgumentList;

class MexFunction : public matlab::mex::Function {
    ArrayFactory factory;
public:
    void operator()(ArgumentList outputs, ArgumentList inputs) {
    double sm = 0;
    const TypedArray<double> inArray = inputs[0];
    for (auto& elem : inArray) {
        sm += elem;
    }
    outputs[0] = factory.createScalar(sm);
    }
};

How important is to use the keyword "const" in declaration of inArray ? Will there be performance difference if I omit it ? I use following function in MEX module which is called from MexFunction::operator():

void Initialize(TypedArray<double> x, TypedArray<double> y)
{
    ...
}

void operator()(ArgumentList outputs, ArgumentList inputs)
{
    ...
    Initialize(inputs[1], inputs[2])
    ...
}

Should I declare the input arguments of Initialize function as const to improve performance ? Problem is that code can be compiled and run without problems but I don't know what happens under the hood. If possible I want to avoid uneccessary allocations and deallocations. Especially if it is that simple like adding one keyword. In other projects unrelated to MATLAB i use references or pointers where possible if the underlying data type is complex. What is preferred way to pass data in MEX modules ?