EEPROM Library Lenght Read

Hi,
I added cli() function to code line. Then, i added the int eepromLenght = EEPROM.length() code. Then , I printed serial terminal, it came eepromLenght= 10. I use without cli(), it come eepromLenght= 1024. Why?
I didn't understand.

#include <EEPROM.h>
void setup() {
 // put your setup code here, to run once:
 cli();
 int eepromLenght = EEPROM.length();
 Serial.begin(115200);
 Serial.println(eepromLenght);
}
void loop() {
 // put your main code here, to run repeatedly:
}

What do you think "cli()" does?

...and how do you think serial I/O works?