It is indeed (although "receiving
absolutely no light" is never the case unless the light is off, else you wouldn't be able to see the leaf either). Look into mobile vs immobile plant nutrients, just a random example:
http://masteringhorticulture.blogspot.nl/2012/01/mobile-vs-immobile-nutrients.html and xylem and phloem translocation from sources to sinks.
http://www.biologyreference.com/Ta-Va/Translocation.html
Translocation is the movement of materials from leaves to other tissues throughout the plant. Plants produce carbohydrates (sugars) in their leaves by photosynthesis, but nonphotosynthetic parts of the plant also require carbohydrates and other organic and nonorganic materials. For this reason, nutrients are translocated from sources (regions of excess carbohydrates, primarily mature leaves) to sinks (regions where the carbohydrate is needed). Some important sinks are roots, flowers, fruits, stems, and developing leaves. Leaves are particularly interesting in this regard because they are sinks when they are young and become sources later, when they are about [make that very very roughly]
half grown.
As you can see the nonsense some defoliators claim about leaves costing energy (which is the same as claiming they become sinks) is just that, nonsense. Of course to create a new leaf energy is required captured by other leaves, they start out as sinks, but once it created enough chlorophyll to perform plenty of photosynthesis to capture enough energy for itself to grow larger and have energy left to spare with other new leaves/buds/roots it becomes a source. After the transition, during flowering, they are all sources (of energy and indeed reserves).
It also goes a little further than pouring nutes down the sink, the 'nutes' in the leaves are already processed ready to be transported and used. So in a way, you'd also be pouring light (electricity, money) down the sink. Now imagine a LED grower who defoliates
