Why are F-15s usually taking off with afterburners?
To be sure to not use more runway than available.
It is also good to have runway to spare in case take-off has to be aborted.
Look at this image as an example from another fighter. Notice the two X-axis. The top MIL is for without afterburner and the bottom FULL AB is with afterburner. Notice how the numbers for the MIL is almost double that of the FULL AB axis. That means much (a little less than the factor difference between the two numbers) more runway required for same conditions. And in case your wondering, that number depends on runway temperature and altitude above sea-level beside from thrust setting.