Yes: it is easy to carry a virtual machine to anywhere (even to a different host operating system) provided you have a data carrier big enough to hold your virtual machine including all data stored there.
No: you will likely not be able to get hold of your virtual machine in case your laptop has a hardware defekt.
Only reliable solution: Backup your data frequently
Possibly: There are few situations where an OS residing in a virtual machine may be of advantage in the follwing cases:
- Carry a system to another computer where it is not possible to restore backups (e.g. because we do not want to install the OS).
- A highly customized OS where restoring and reinstalling may not be accomplished easily.
- Small virtual machines that can be saved and restored in a sensible way.
- Running an OS that can not easily be restored from backups on different hardware.
It may therefore be that when you are running a fairly customized Windows in a virtual machine it may indeed be faster to restore your working enivronment on different hardware.
In case you are not running applications that demand a poweful graphic card, and running the virtual machines on a host with enough RAM to spare for the virtual machine then you may not suffer from much loss of performance. Modern virtualalization solution are doing a very good job at this.
Note that incremental backups from your virtual machine can only be done from the virtual guest as the files on you virtual hard disk are stored in a single file on the host that will have been changed on every boot. For easier backups it may also be a good idea to save your data in a shared folder on the host machine. This will enable incremental backups and also will keep your virtual hard disks small.