I would have to say overfeeding is much worse. Our whole plan is to grow plants and mimic the natural growth cycle provided by nature as best as possible. In nature, plants are never fed, they simply soak up all the nutes in soil provided by nature. Plants in nature also never come in contact with nutrient burns. Dont be mistaken, feeding plants can be extremly benificial when done coorrectly but once burnt, it can take uo to wees to recover. As for underfeeding, some sure signs of that may be short underdeveloped limbs, discoloration and a all around "sick" look. Simple solution, give em a bit of food and you will see recovery in as little as 1 day. Overfeeding weeks to recover,,,underfeeding a few dyas to recover. I would always say underfeeding is better. A safe way to avoid both, when you feed be sure to use 1/2 or 2/3 of the doseage. NEVER use the recomended dilution until the plants have reached atleast 1 1/2-2 months old. and ait until about 2-3 weeks old before the 1st feeding. Most soil will have enought food to cover them fr the 1st 3 week period. After that 3 weeks period feed with every other watering or once a week. At the 1st sign of burn i would briefly flush the container to remove the excess nutes. Keep in mind the burns always start from the roots up. Once you notice burns, you should lay off feeding till those burns heal or show themselves as unhealable( if they show no sign of healing and onlg get worse, dry brittle or a orange/brown color) then trimming those limbs off would be the best option, hope that helps you get a better understanding----------------------------------------420