In fact rank, point and karma all play an important role for your account. Your account activity will increase with your daily posts and points will also increase. Karma proves the quality of the posts you create. If your post quality is good you will get lot of karma. This karma will help you a lot in future because when your account rank sr member then you can participate in signature campaign. If your karma is high then all managers will give you the opportunity to participate.
In addition to this op, while positive karma is a kind of appreciation you get from members for creating useful posts or contributing positively to discussions, you still risk losing the number of karma you've accumulated if you get a negative karma from a member or members. When you get a negative karma, your overall karma reduces. This is not a good sign as it will be giving you a negative reputation.
You may get a negative karma when you spam the forum, when your account is flagged or when your posts are not helpful at all.
So, while you try hard to rankup, you should also pay attention to your reputation.