Its a major issue and will affect the weight and quality of the harvest. No leaves = light weight and a crap smoke in general. Its very important not to overfeed right from the beginning to avoid having no leaves left at a crucial time flowering and late flowering. The leaves are drawing energy into the buds so they can develop.
Currently i have a nice big G13 with a few weeks to go that is green from top to bottom with buds everywhere, no burning not even the tips of leaves.
The real "food" for your plant is light. Your plant produces energy from light through a process known as photosynthesis, which is most effective when the plant has healthy green leaves.
Your leaves are like solar panels, and the energy produced by the leaves is used as energy for the whole plant. You need the leaves to be in tip-top shape to get the most energy from the lights, so your plant has plenty of energy to grow and produce buds.
Therefore, the biggest problem with nutrient burn is the fact that you are losing leaf mass and overall leaf robustness on your cannabis plant.
A little nute burn won't slow down your plants much, if at all, but if nute burn is left out of control, you will begin to lose serious leaf mass and it will dramatically slow down plant growth and reduce your overall yields.
What's worse, if excess nutrients are not flushed out of the plant's system before harvest, the buds may contain trace amounts of extra nutrients, giving the buds an unpleasant chemical-like taste. Speaking of the flowering stage.