I dont like it near the center, it heats the whole cage.
That may be a good thing depending on your situation though.
Having it in a corner maximizes the use of space in the enclosure, and makes it easier to get a temperature gradient going.
If its in the corner, one can simply place a vine/branch going from that corner, towards the dead center of the cage. This makes it easy for the chameleon to choose its desired temperature, as all it has to do is move up, or down the branch.
(this pic was made to explain how I set up a jacksons cage, but it gives a visual of what Im talking about basking-wise.)