There is no rule of thumb here.
It's all a matter of personal preference and what the desired outcome is.
What is good to one person may not be good to another.
That does not mean anything is correct or incorrect.
It's just a matter of what makes you happy.
The stepover ridges could be laid out to see the ridges, but there will be ridges even if you cannot feel them.
The smaller the stepover the smaller the ridges.
At a 2% stepover the ridges are so small that they are almost not there.
Then it also depends on the diameter of the ball nosed end mill.
The larger the diameter, the flatter the nose of the end mill will be.
The smaller the ridges and the more forgiving the stepover is.
Another thing to consider is time. If a job is going to run for 4-5 hours and I am just putting around the house and yard and I can pop in to check on the machine - I don't care that it took a long time.
On the other side of the coin, if I have a 5% stepover and the finish is going to take 18 hours and I am not going to be watching it, I will adjust the parameters to get a reasonable cut time and compromise of the quality
Personally, I just hate a fixed rule of thumb.
I find it better to understand and adjust according to my needs or desires.
Like I said - I can be very very anal about this stuff.
I can tend to be a bit less practical.
Imagine the Possibilities of a Creative mind