peter - it's called "concentration" (as opposed to "diversification"), and it limits the chances of an error... in other words, if you have two positions open, you have doubled the possibility of making a bad trade... also, less stress since it simplifies your exposure... I do it fairly often with good results... for example, I am much more comfortable with nothing but oils, even though I am very tempted to buy some BGO, GOOG, SIRI, etc...
"MELT-UP" TIME!!!