When I put the mouse over it shows these:

When set, the RealTracks will play a simpler arrangement
(less busy, less embelished).
See the RT column for
availability of Simpler RealTracks.

So can I also understand that if I check "simpler"
Then it can be used as intro, verse
If I don't check it, it can be used as chorus.
I mean audibly, checking "simpler" makes the generated WAV feel simpler?

You should try it and listen to the results.

You need to also only select tracks with an 's' in the Simpler column.

From the Help:
- "Simpler Available" will have a letter "s" in the column if the RealTracks instrument has simpler options available. These are parts with less busy, less embellished playing for generating simpler arrangements.

I'm probably like a lot of others here. why don't you just try it and see?

I tried it. There is a little difference, but not a big difference

I tried it. There is a little difference, but not a big difference.
I'm worried if I'm missing some setup trick feature, so I'm here to discuss it.

My experience is that there is usually very little variation in the Simpler variations.
In one or more tracks, 'simpler' actually delivers silence, (but I think that's a bug).