Ultimaker 2+ Extended Z Height 312mm, not 305mm

[RetromanIE 41]

So the official height of the Z axis on the Ultimaker 2+ Extended is 305mm. Using the S3D machine control panel I was testing the x and y axis sizes as I was having a centering issue(which i now understand).  While i was at it i decided to see what the actual height of the Z axis is, which on my machine is 312mm!

I did a test print to see if i can actually print that height and it does indeed go up to 312mm without issue(was a quick vase mode print). Is there any technical reason for not using the extra height? I mean it's only an extra 7mm, but that could be useful for tall prints without having to resize or split etc.