Every "space" ("model space" and "paper space") in AutoCAD have their own limits, and these limits have different uses in each "space". They are totally independent one from the other and you have to define them when being in the corresponding "space" (you cannot modify model spaces' limits through Paper Space).
In Model space.
Model Space limits are used to tell AutoCAD what part of the drawing should be included by priority in the drawing's memory. (The part of the drawing included in the drawing memory does not need view regeneration).
For instance, you have probably witnessed arcs and circles, drawn far from the origin of the drawing, represented as polygons. You have to regenerate the drawing to get the correct smooth representation. If you define the limits of the drawing large enough to include these arcs then AutoCAD will try to include them in the drawing's memory so that you do not need to regenerate to get them drawn correctly. This concerns only the view representation the accuracy is not altered by the limits command.
This is very useful when working with very large survey drawings. In that case you define the limits on the smaller area of the drawing where your project is placed, in order to tell AutoCAD to include your projects' geometry in priority in the drawings' memory and not the totality of the survey's geometry.
Limits are invisible but you can "see" them if you set your grid "not to display" beyond limits. When using the zoom command with the option "All" AutoCAD will zoom to the drawing limits as opposed to the "extends" option that will zoom to the extends of the drawn geometry.
However setting limits is not mandatory. Most of the times the drawing memory is large enough for all the geometry including element outside the model Space limits. I personally believe that is best practice to set the limits
In Paper Space.
Paper space limits are used to define the paper size (what is represented as a white page). So it is better to modify them trough the "page setup manager" by choosing the right paper size. You could use the limits command in Paper Space but will have no effect other that reporting the coordinates of the paper size. You will notice that the lower left point o f the paper spaces' limits is never the origin of the Paper Space. This is because the origin of the Paper Space is the corner of the printable area (represented as a hidden line rectangle) and not the paper corner for obvious cut and paste reasons between different paper sizes.
I do not see why the limits command would be limited in a trial version unless this is a bug. Are you sure you are midifing the right limits
Hope it helps
Aghis
