In Becker et al (2011), the authors increase the expression of several genes through different methods. For some genes (e.g., lysA, ddh), they achieve overexpression by integrating an additional copy of the gene and its flanking regions. On the other hand, for other genes (e.g., lysC, dapB, fbp, and the tkt operon) they take another approach and instead replace the native promoter with a strong constitutive promoter (Psod or Petfu).
Is there an advantage of one technique over the other? Why was one technique preferred over the other one for certain genes?