if i import a poser figur fromposer pro in to vue 6 infinite I get an option to use poser shader tree if i use that most of the time my system resources fall low what difference does it make and which is the best to use?

This topic has been debated already several times in this forum. I would say this is a matter of taste. There are several people who prefer the look & feel of characters rendered with the Poser shader tree. Other people prefer the look & feel of SkinVue. Others use neither, just a normal import. Each person will have a different opinion.

If you use the Poser shader tree, you'll get a render where the character will look very similar to what it would look like if it was rendered in Poser. But you must bear in mind that some more complex Poser shader nodes are not correctly translated to Vue, so you might not get exactly what you expect, in some cases. You also have no possibility to do fine material adjustment in Vue.

If you use SkinVue, you'll get a render where the character looks very different and very realistic and you'll have the possibility to do fine adjustments in Vue, until the character looks exactly like you want. Of course, you have to buy SkinVue.

If you use neither, you can still do material adjustments in Vue. You'll have a lot of things to change until the character looks realistic, but it's possible, of course.

In my experience there isn't a significant difference in quality when I use the Poser shader tree. Some people like it though. You could do a few test renders on figures to see if you can tell the difference.

Of course, if your resoruces are falling low, it's probably not worth it. 

If you want a laugh, try posing a Poser figure inside Vue 6 Infinite. It would slow a super computer. 

There are two issues when using the Poser shader tree option in Vue:

1. Performance:  The Poser api is not threaded and is a very large resource.  It therefore, must operate in the primary render thread of Vue which will lower system resources.  For most rendering tasks on 32-bit platforms this is not a problem, but for posing, it's a big problem which is why there is so much latency.

2. Realism: Unless the Poser shader tree is very simple, you are never going to get a perfect  match in Vue with what you render in Poser (as explained by Rutra above).  You can still get decent results, but if you are aiming for higher levels of realism, you are better off using the native Vue materials/render engine. 

Better to tweak to taste as Vue materials, by far :)
see my Poser import tutorial.