A few questions after a new install on Arch

I installed openframeworks through archlinux’s user repository and I think it installed it to /opt/openFrameworks. When it finished it told me to run /opt/openFrameworks/scripts/of-make-workspace which generated ~/of-workspace.

I proceeded to try to try to run make in ~/of-workspace/examples/graphics/imageSubsectionExample but I get the following

Compiling OF library for Release
make[1]: Entering directory '/opt/openFrameworks/libs/openFrameworksCompiled/project'
make[1]: Leaving directory '/opt/openFrameworks/libs/openFrameworksCompiled/project'

Compiling imageSubsectionExample for Release
make[1]: Entering directory '/opt/openFrameworks/examples/graphics/imageSubsectionExample'
mkdir: cannot create directory ‘obj’: Permission denied

But runs fine when I do sudo make. Also why when I ran make for the first time it took quite long, but now only 10 seconds or so?

Later on I created my own project with the projectGenerator and now I don’t need to prepend make with sudo. Why is this different?

why did you install OF archlinux’s user repository ? .
and probably is because the project generator was already set with sudo or something like that
you could just download OF and compile your self