Principal - Reverse - Flatten - Graft - Simplify

Hi guys, often I use to "play" with this commands from the components menu in order to get right my algorithm, the truth is that I still don't understand their meaning. 

For example. In a split list I wanted to divide a list of rotating planes (really easy) and just when I "flatten" the list it worked out. Before the list was no longer splitting. 

JUST WHY ?

tnks 

Alessio.