Hi Jyoti Raina
Welcome to the forum. Since in practical conditions we do face problems like dispersion and attenuation of signals. So u have to enable it in order to make your system practical enough . U would be running your system in ideal conditions if you disable it. And by the way u have many techniques for dispersion compensation and to reduce attention. You should opt for those techniques to get better result. Hope it helps.
Regards
Burhan