What does a call to 'this->template [somename]' do?

Here is an example where this->template is required. It doesn't really match the OP's example though:

#include <iostream>

template <class T>
struct X
{
    template <unsigned N>
        void alloc() {std::cout << "alloc<" << N << ">()\n";}
};

template <class T>
struct Y
    : public X<T>
{
    void test()
    {
        this->template alloc<200>();
    }
};

int main()
{
    Y<int> y;
    y.test();
}

In this example the this is needed because otherwise alloc would not be looked up in the base class because the base class is dependent on the template parameter T. The template is needed because otherwise the "<" which is intended to open the template parameter list containing 200, would otherwise indicate a less-than sign ([temp.names]/4).