Identifying the cause of a file taking 2 mins to open and paste from also taking ages?

[wim (Wim Dekeyser)]

Steve -

@Steve1

In a new file attached, created by ‘export selected’ then opening that file, take the indicated blue curve and copy paste into same file, takes 8 secs, why ?

FWIW, it’s instant here on the Rhino 8 WIP that I had open.

@Steve1

so what does ClearAllMeshes do ?

It deletes all display meshes for all objects and will put all your viewports in the Wireframe mode.
For further reading, check the help file.
-wim