does this mean that where I have always ensured in the Unity editor that the ARCamera preview had the imagetarget in sight this is in fact....not necessary
Correct. If you think of it, the relative position of your actual target with respect to the ARCamera will entirely depend on how and where you actually place / move the physical (e.g. printed on paper) target with respect the the device camera of your phone/tablet/webcam... and in the real world, this won't have much relation with the artifically 'frozen' relative positions that you have set in the Scene in the Unity Editor.
However, keep also in mind that there are situations where the position of a Target and/or the position of the ARCamera in the scene may matter, e.g.:
- if you are using "World Center Mode" = CAMERA, the ARCamera position in 3D space will not be updated by Vuforia, while the Trackables positions will be updated so to match their relative position w.r.t. the Camera; in such a case, you may want to set the ARCamera position at a location that makes sense for your App; for example, in a mixed reality App like the AR-VR sample, in which you start in AR and then move to VR, the position of the ARCamera is basically matching the position of the User Head in the VR virtual world, so you'll want to set it at a position that allows the user to be correctly placed in the VR world when in VR mode
- if you are using "World Center Mode" = FIRST_TARGET or SPECIFIC_TARGET, the position of one or more of your Trackables in the Scene may be important, for example you may want to set them to a location that makes sense with respect to other 3D assets present in your scene
Hope this helps.