I did NOT say that you have to compile anything. I said that Virtualbox
takes care of it for you. If you install Virtualbox and have the terminal
window open you will see what I mean. It will tell you what the install
script is up to. This is a good practise anyway as it shows you things that
you would otherwise miss. I think that build-essential is part of the
default Ubuntu installation, but it did not used to be. I really don't keep
track.

In the past if you did not have build-essential installed then the
installation would seem to work, but when you clicked on the icon to start
Virtualbox, nothing would appear to happen. If you then ran virtualbox from
the commandline you would see an error message that you need to run a config
script. Nothing would happen if you ran this script until you installed
build-essential first.

The modules I referred to may or may not need to be compiled. It is just
helpful to have the tools pre-installed in order to avoid an incomplete
installation. It used to be that VB would compile modules for your current
kernel/ headers. I think that it now uses dkms and these do not need to be
changed as your kernel changes. But since some people here are working on
older versions of Ubuntu, I threw that info in. It pays to be prepared and
cover all of the bases.

I admit the installation process is much streamlined these days. I used it
when it first came out from Innotek and have seen much improvement over the
years. I used VMWare before that and would never go back. :) I think that
you still need to ad your user name to vboxusers, at least according to
Virtualbox documentation.