What are the advantages of offset tweeter location

Rather than an advantage, I'd say it's a matter of design. The tweeter offset is usually intended to help correct phase and control diffraction.
There are also lobing matters that seem to enter the game -- but I'm not sure about the offestting's effectiveness at those frequencies.

Offset tweeters result in unequal, or staggered, distances from baffle edges, hopefully preventing reradiation from summing lumpily. Also can allow more flexibility in setup, as you can compare tweeters in vs out, very helpful to balance room sidewall issues. Manufacturers tend NOT to ofset tweeters anymore as this requires making/inventorying twice as many boxes, and sometimes expensive tooling or molds use to make front baffles.