Ive been importing figures from vue as pz3 files ,is there any advantages/ disadvantages in exporting them from poser as obj or just save them as VOB after they are in vue can any one explain what difference it makes .(in particular to speed/quality of the finished render) many thanks in advance

Import the pz3, tweak your materials unless you want to use the Poser shaders, save as vob if you intend to reuse for another scene or use in ecosystems.
If you use the Pose shaders, I'm not sure you can save as vob.

will a vob use less mem will it look any different when rendered?

If you save as vob, it will look different than using the Poser shaders, because if you use the Poser shaders, Poser will do the rendering, not Vue. This option requires double amount of ram, so you need a strong system.
If you don't use the Poser shaders, you will need to fiddle with materials a bit, for example Poser uses the colour black for highlights, very specific to Poser ( it's actually the only program I know that uses black for highlights), so you'll need to modify not only the colour, but the amount and shininess as well. Some materials import reflective, when they aren't in Poser, so you'll need to look into this as well. If there are specific shaders in the Poser materials, they may not import correctly in Vue, if at all. Most of the new figures use special functions to create realistic human skin, and they may not import well in Vue, or you'll need to recreate the effect in Vue ( bump, specular & displacement maps for example), which means you'll need a good knowledge of the advanced material editor and the function editor.
Any other 3d format will be the same, only the texture maps will import (in Vue or any other app for that matter).
Now when saved as vob, you can't use the Poser shaders, you'll need to convert all material channels that did not import, but it's a fact that vob will use a lot less memory.

Check my Poser import tutorial in my signature ;)

Plus many figures have "no shader" MATs which tend to import better.

Shaders are very dependent on the render engine, so they don't translate well if at all.

thanks for that thats been most helpfull though as im still a bit new to vue the advanced material editor looks a bit daunting ill have to spend some time studying it but any way thank you all for your help