Itachi explained that having the actual kekkei genkai makes it much easier to use the Sharingan that someone who does not. When the Sharingan is not being used by someone of the kekkei genkai, it requires much more chakra than normal. Kakashi is a great example of this. Despite both having been stated to have low chakra and stamina, Itachi is able to have his Sharingan activated a majority of the time, but Kakashi is left nearly exhausted after using it in a fight. Also kekkei genkai-users are able to deactivate the Sharingan, and other Sharingan users, like Kakashi, have to cover up the Sharingan because it will not deactivate and continue to consume chakra. Kakashi seems to have improved his stamina and chakra levels, to try and dissipate the weaknesses, but they still exist. Also the Sh