When c macros are expanded why does the code get so big?

I've been experimenting with C's macros, and decided to expand them to see the replacement. When I supply gcc with -E, I get 800 lines of code just for this simple code:

#include <stdio.h>#define TEN 10int main(void) {    printf("hello world %d", TEN);    return 0;}

My questions:

• Why do I get so many lines!?
• How can C run so fast with that many lines?
• Is that many lines a problem?