a few extra bits you may find handy:
You cannot use split poly between two edges, if there is one or more inbetween then. It needs to be done a bit like a join the dots picture, hopping from one edge to the next untill you have split all you need.
The split poly option box gives a nice feature of being able to change the magnet strength. In other words if you just want a quick split at exactly midway between two points set the magent tolerence much higher than default. This will mean your click will be moved exactly to the middle or ends. Set the tolerence lower so you can control in more detail where the split will be made.
To see what I badly explained, create a new plot cube and try to split a face right in the middle. Once with low tolerence, then undo and try with much higher tolerence