"has no collision geometry (Will be slow)"

So i just ignored this warning and thought "what ever"

Does someone know what it exactly means??

It means a model that has no collision geometry is beeing munged.
In that case, a collision geometry for that model will automaticly be created, which takes some time. Thus, the munging of that model will be slow.

Nothing to worry about.

Well but auto collision is expensive/and not accurate. Its much better to import the msh in xsi and a lowrez Collision Mesh. just add a mesh with the name _collision for static meshes or a primitive for animated meshes

Just add -nocollision to your .msh.option file.