Should I use another user than the root when installing NGiNX

How are you planning to install these applications? Since you say you're using Ubuntu, then I would assume that you'll be installing apps via either the graphical manager or by apt-get or aptitude.

If you're using the graphical program manager, then it should prompt you for your password; this performs a sudo under the hood.

If you're using either apt-get or aptitude or something similar, those programs need to be run as root to install.

In both instances above, the installation scripts for the packages will (should) handle any user-related issues that are necessary for the program you're installing to function properly. For example, when I did an apt-get install jenkins, the installation scripts automatically created a jenkins user for me, and my Jenkins CI server runs as the jenkins user automatically.

Of course, if you're compiling all of these programs by hand, all bets are off and you'll need to figure out how best to do all of this yourself. Of course, if you're compiling these programs by hand to get them installed, I'd have to question why you're using Ubuntu in the first place; one of the best parts to using a Linux distribution with sane package management capabilities is actually USING said package management! (Note: by this statement, I mean anything Debian-based for sure; and I understand that Red Hat's yum provides very similar capabilities, but I haven't used anything RedHat since around 2003.)

You don't want a process to have any more access than it needs. So yes, you should use a user besides root -- one that has the minimal privileges required to read the files it needs. Typically this involves creating a new nginx (or www or similar) user specifically for the task.