General enhancing (a fancy name for adding stars to your General) is an important part of developing your Generals strengths, as it increases the base stats.
Image of Mt Coonowrin (Glasshouse Mountains), Queensland, Australia.
To increase the base stats, you need to enhance (add a star) to your general, which is limited by the level of your general, which in turn is limited by the level of your monarch (your general level can never be higher than your monarch level.) The first star requires a minimum general level of 5, the second at LVL 10, third at LVL 14, fourth at LVL 18 and the last star can only be added at general LVL 22.
There is no benefit or loss to whether you add the star when your cultivate stats are close in value to the base stats, or whether there is still a lot of cultivation to be done.