Most modern VMs are configured to skip the GRUB bootloader for a seamless experience. However, you might need to access the GRUB menu at times. For example, if you want to switch back to the older kernel or get into recovery mode for resetting the password.
It is certainly also a useful way to test any changes to GRUB before doing so on your production machine, too. In this way if for example you'd like to add colour themes to your main machine's GRUB, test it out first on the VM's GRUB until you have it like you want it, then apply to your main machine.
See How to Access the GRUB Menu in Virtual Machine
Need to access Grub while using Linux in a VM? Here's how to do that.