ios::sync_with_stdio(0);cin.tie(0); why?? code example

Example 1: ios base sync with stdio

ios_base::sync_with_stdio(false);
cin.tie(NULL);

Example 2: ios_base::sync_with_stdio(false);cin.tie(0);

//For faster I/O in Competitive Progtamming in C++.
ios_base::sync_with_stdio(false);
cin.tie(NULL);