Use this to reduce your face count.
Note: You can only have one face marked at during this command. 

This will flip all marked faces.
 

Checks marked faces for planar then offers to split them into triangles for you. The new faces created gets sample texture so you'll have to touch them up.

Great for fixing smaller faces but you have no control of how it splits the face.

With 4 verts and a shallow bend in the face it may not matter.

If there are 5 or more it could get messy (see Ex. 3).  Only a part of the face needed to be split.  The next 2 tool "Splt Current Face"  Triangulate Current Face"will give control over splitting.

Creates an edge that connects the 2 marked verts. 

You can use this on planar and non-planar faces

Pick the tool the get the results below.

This will divide a face into triangles with new edges coming  from the current vert. 

You can use this on planar and non-planar faces.

This splits all marked the same as Face Planar Check but without checking first and offering.  It finds all the marked faces that are non-planr and triangulates them.