Your leaf structure is one of the easier ways to get feedback and early warning signals from your plant on how it is doing. The goal is a perfectly flat leaf. If you over-water in soil you will get a gently curved structure from back of leaf all the way to tip. In hydro it is an indication of not enough O2. Clawing (a sharply downward hooked leaf tip) indicates the plant has been over-fed, often too much nitrogen. Upward hooked leaf tips or edges is often a sign of heat distress.
So you read your leaf structure and then look at what your feeding levels are and try to draw some conclusions on whether you should feed more or less. If your ppms are reasonably high you can usually rule out a deficiency and assume you have a lockout from bad ph or from overfeeding. Too much of one element will lock out nutrients, google nutrient antagonism charts to see how the relationships work.