The location of the installation of the content depends on the OS. There can be differences between OS X and Windows. In any case, the Studio default location is only a suggestion. Personally, for example, I don't use it. I keep all my DS content in a very structured directory, under ~/DSContent (~ symbolizes your home folder) path.

When it comes to using both Poser and DAZ Studio I advice to actually duplicate the content. For example, I have V4, and all connected accessories both under ~/DSContent and under ~/PSContent, where PSContent is the home for all Poser content. Trying to keep a single copy shared between applications is going to impose constraints to either one application or the other. If you organize the content to be optimal for DS then you will likely have sub-optimal organization in Poser and viceversa. The best option is to keep two separate repositories and organize them as it's best for each application.

Cheers.

Paolo

https://www.preta3d.com
FB: https://www.facebook.com/RealityPlugIn
Tw: @preta3d
G+: https://plus.google.com/106625816153304163119
The Reality Gallery: https://reality-plug-in.deviantart.com