I use EAC with Ogg Vorbis and I don't know much about the technics behind Ogg Vorbis/EAC but everytime I read "I use this command line, I use that command line" but without a command line it works too. So, why should I use a command line?

A command line allows you to include tags, choose the quality parameter and fine-tune the options to your wishes. When they say "use this command-line" for EAC, it probably includes the artist, album, track number and similar switches for storing in tags, plus the just barely avoidable quality switch (-q). The quality switch allows you to select the desired quality of your files (defaults to -q3, which targets the ~110kbps range I think).

Sure, you can encode without parameters, but you get a bare-bones Vorbis file, without tags and limited to the default quality level.

I set up EAC according to the instructions on the "Essential Ripping Guide for EAC and I use this -q 5 -G "%m" -t "%t" -a "%a" -l "%g" -d "%y" -N "%n" -c "comment=EAC Oggenc 1.1.0 -q5" -o %d %s commandline.
If I remove the commandline and change "user defined encoder" for "Ogg Vorbis encoder" and set the bitrate to Q5, it encodes at Q5 and I get all the tags that I have set. If I change to Q7 it encodes at Q7. Don't shoot me, I can't help it

We need somebody to write an article in the wiki who uses EAC and is familiar with configuring Vorbis for it so we can have that added to knowledgebase. I would do it, but I am not familiar with EAC all that much although I am sure I could read about it.

Great, so that works for you. It would work for me, too.

But should you desire to use -q 4.357 or some other additional command-line switches, you'd need to switch to "user-defined encoder" in order to be able to provide them to the encoder.