TCGA level 3 data is the normalized segmentation values where the value 0 means diploid state of the chromosome. Any positive value means amplification and negative means deletion. We must remember that in a copy-number gain or loss event, a large segment of chromosome (or even whole chromosome) is amplified or deleted which often contains multiple genes. The CNV normalized values -1 or 1 are the low confidence events which could often be an artifact. These values can sometimes introduce noise during analysis so usually only high confidence values are used.