Slicing multiple objects and moves between objects

I just tried printing 5 objects when calibrating the printer and i noticed that slicer first printed the inner perimeter (a hollow cube with 3 perimeters) for all 5 objects, then the middle for all 5 objects and last the external perimeter for each layer. Is there any valid reason to do it this way instead of finishing the layer for one object at a time?

Btw I'm using slicer 0.9.10b

Cooling would be one reason. If the head keeps touching areas just laid down that are still hot then it's possible to get distortion of print by keeping the plastic molten. It may not show up on the first few layers but eventually it would just push material around like a spoon in pudding. By 'taking a break' and switching to another part or another area of the same part it can give the freshly laid down plastic time to cool and firm up.

If you want to see what would happen print a 10mm cube (just one) and make sure cooling is turned off. The base will be ok but further up the cube it will start to just push around already laid down plastic until it no longer looks like a cube.

The cooling would be as good (probably even better) if you finish the layer completely for each object before moving to the next one, and there will be less risk of oozing.

Slic3r shouldn't do that - maybe you could try v0.99

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Waitaki 3D Printer

I have seen the same thing and it drove me nuts and resulted in a lot of extruder jams. What you want to do is check the little box in the settings that says "avoid crossing perimeters". It is in the print settings tab, layers and perimeters page, all the way at the bottom. When you check that it will force slicer to complete each object layer before moving to the next object on the same layer.