On day of judgement if you have backbitten someone your good deeds will given to that person or if you don't have good deeds you will take his evil deeds. We all know everyone backbite, it's difficult to be free from it or any other sins. Also there is no guarantee if you have a lot of good deeds you will enter Jannah so is there any point of doing good deeds? I am not telling anyone to stop doing good deeds, just asking a question to increase my knowledge.
Brother, doing good deeds is very important because it may erase bad deeds, and increase your position in jannah, in shaa Allah. You'll (likely) regret the moment you missed the chance to do a good deed, because those will very likely change your life ETERNALLY. Know what's light on the tongue, yet heavy on the scale on the Day of the Judgment? Dhikr, and the best Dhikr is the Holy Quran.
And Allah knows best.