Long term effect on Mac computer of installing Windows/Running a Windows VM
There will be zero issues running Windows on a Mac.  A Mac is basically an Intel based PC. 

If you are using a VM, regardless of the platform (VMware, VirtualBox, etc) once you delete the virtual machine, it's gone.  Unless you share folders between the VM and the host, there is nothing that goes outside the VM container.

If you are using BootCamp, once you delete the BC partition, Windows will be gone.