Recommended way to insert elements into map

Possible Duplicate:
In STL maps, is it better to use map::insert than []?

I was wondering, when I insert element into map, what is the recommended way. Should I

map[key] = value;

or

map.insert(std::pair<key_type, value_type>(key, value));

I did the following quick test:

#include <map>
#include <string>
#include <iostream>

class Food {
public:
    Food(const std::string& name) : name(name) { std::cout << "constructor with string parameter" << std::endl; }
    Food(const Food& f) : name(f.name) { std::cout << "copy" << std::endl; }
    Food& operator=(const Food& f) { name = f.name; std::cout << "=" << std::endl; return *this; } 
    Food() { std::cout << "default" << std::endl; }
    std::string name;
};

int main() {
    std::map<std::string, Food> m0;

/*
1) constructor with string parameter
2) copy
3) copy
4) copy
*/
    m0.insert(std::pair<std::string, Food>("Key", Food("Ice Cream")));

/*
1) constructor with string parameter
2) default
3) copy
4) copy
5) =
*/
    // If we do not provide default constructor.
    // C2512: 'Food::Food' : no appropriate default constructor available
    m0["Key"] = Food("Ice Cream");
}

1. I realize by using member function insert, less value's function call will be involved. So, is using insert a recommended way?
2. Why default constructor is needed, when map[key] = value way is being used?

I know that insert doesn't overwrite existence key value pair, but map[key] = value does. However, is this the only factor I take into consideration, when try to choose among the both?

How about

1. Performance
2. Availability of value's default constructor
3. ???