Single Quad from Edges
Select two contiguous edges and run JJ_SmartQuad and a new quad will be created in the same plane.

Row of Quads with Connect
Here a whole row of edges has been selected and the connect option used so that the new quads are created and then hooked into existing geometry.

Note the L shape of the selection which is acting as a guide for the quad placement (more on this later).

Row of Quads with Connect Around Corners
Here you can see that JJ_SmartQuad will 'go around corners'. More simply it will follow the contour of your edge/point selection. However, when it goes around 90 degree corners it doesn't create an extra quad to preserve the integrity of the grid's topology (hopefully in a later version).

Again, notice that there's an L Shape at one end of the selection. This is crucial to let the tool know where and how it should be creating quads.

What constitutes an L Shape
In this example you can pretty much see how JJ_SmartQuad attempts to understand your selection. It looks at either end of the selection and then makes a judgement on where the L Shape starts and then fills in the quads on that basis.

The L Shape doesn't have to be defined by an additional polygon - just by a change in direction. The tolerance is very, very small so you could create incredibly thin strips of polys this way! If you were crazy enough to do so...

Unconnected
JJ_SmartQuad installs two commands:
JJ_SmartQuad and JJ_SmartQuadC. The former generates an unconnected  poly/row of polys where the last vertex is not joined to existing geometry. See right.

Connected
The second command - JJ_SmartQuadC -  generates a poly/row of polys where the last vertex is connected to existing geometry. See right.

Connecting to Adjacent Geometry
By using connect you can 'force' the new polygon out of planarity and to connect to the nearest vertex.

Limitations
If you end  up using SmartQuad there are going to be times when you don't get what you expected. The script tries to interpret the 'flow' of the topology by looking at the angles between adjacent polys. If your mesh is irregular then SmartQuad is likely to return irregular results.

You need to be careful not to confuse SmartQuad with ambiguous selections  i.e. where you have an L Shape at either end of the selection, for example or if your selection could be interpreted as looping around itself.

Most importantly, SmartQuad has been designed to only work with regular quad topology - if the edge comes into contact with tris or ngons the tool will find it impossible to assess the poly flow correctly.