SCNT can be inefficient. Stresses placed on both the egg cell and the introduced nucleus in early research were enormous, resulting in a low percentage of successfully reprogrammed cells. For example, in 1996 Dolly the sheep was born after 277 eggs were used for SCNT, which created 29 viable embryos. Only three of these embryos survived until birth, and only one survived to adulthood.  As the procedure was not automated, but had to be performed manually under a microscope , SCNT was very resource intensive. The biochemistry involved in reprogramming the differentiated somatic cell nucleus and activating the recipient egg was also far from understood. However, by 2014, researchers were reporting success rates of 70-80% with cloning pigs  and in 2016 a Korean company, Sooam Biotech, was reported to be producing 500 cloned embryos a day. 
Therapeutic Cloning does not involve making a clone of someone- you don't end up with a cloned person: that's reproductive cloning. Therapeutic cloning involves creating copies of cells to make someone better. The process is described below, but it is easy to get confused if you don't read really carefully. The key point to know is that you are cloning an embryo and using it to grow cells, not a new person. It's all experimental at the moment (2011), although different companies and groups keep making claims that say they have been able to do this successfully with human cells.
In 1894, Hans Driesch cloned a sea urchin through inducing twinning by shaking an embryonic sea urchin in a beaker full of sea water until the embryo cleaved into two distinct embryos. In 1902, Hans Spemann cloned a salamander embryo through inducing twinning as well, using a hair from his infant son as a noose to divide the embryo. In 1928, Spemann successfully cloned a salamander using nuclear transfer. This involved enucleating a single-celled salamander embryo and inserting it with the nucleus of a differentiated salamander embryonic cell. In 1951, Robert Briggs and Thomas Kling, using Spemann’s methods of embryonic nucleus transfer, successfully cloned frogs. In 1962, John Gurdon announced that he too had successfully cloned frogs but, unlike Briggs and Kling’s method, he did so by transferring differentiated intestinal nuclei from feeding tadpoles (Wilmut et al. , 2000). Gurdon’s successful use of differentiated nuclei, rather than the embryonic nuclei used by Briggs and Kling, was particularly surprising to the scientific community. Because embryonic cells are undifferentiated, and therefore extremely malleable, it was not too surprising that transferred embryonic nuclei produced distinct embryos when inserted into an enucleated oocyte. However, inciting differentiated nuclei to behave as undifferentiated nuclei was thought to be impossible, since the conventional wisdom at the time was that once a cell was differentiated (., once it became a cardiac cell, a liver cell, or a blood cell) it could never reverse into an undifferentiated state. It was for this reason that, for a long time, creating a cloned embryo from adult somatic cells was thought to be impossible – it would require taking long-time differentiated cells and getting them to behave like the totipotent cells (cells that are able to differentiate into any cell type, including the ability to form an entirely distinct organism) found in newly fertilized eggs.