Because site meshes are typically the most complex entities in an ArchiCAD project, by a very large margin (unless you live in Holland of course), SEO operations on them are quite expensive computationally, and successive operations rapidly slow regeneration of cross sections and elevations while editing, on even the fastest machines.
Bewilderingly, meshes STILL don't support materials priority intersections despite this fact, and despite the fact that every single project has foundations that need to cut into the site mesh. So this is not an edge case.
On sloping sites, foundations and siteworks are inherently very complex, and site meshes are inherently very complex even before SEOs are applied, meaning a project of any scale rapidly becomes unworkable, even on top end hardware, as the number of SEOs required keeps expanding to follow the progression of design & documentation processes. Hundreds of objects typically need to interact with the ground.
Highly embarrassing spending $10K on the best PC that money will buy, and half that again on (increasingly) the second-best BIM software that money will buy, to have even the normal requirements and complexities of depicting the actual construction of buildings on actual sites exceed the capabilities of the system, without time wasting and laborious manual workarounds.
PLEASE give some serious love to meshes, as the highest priority. The current functionality is literally decades old, and is so limited that it is completely beyond justification.
Unless and until there is some way found to massively speed up SEO calculations, please at the very least enable materials priority for meshes
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