I am The Speedlighter – but I also of course use available light sometimes. Like in this shot, from my Tumblr feed:

That is an available light shot that works because:

• There is a window with reflected light – not direct sunlight. This means a north-facing window, for instance; or in this case, an east-facing window in the afternoon when the sun is in the west.
• I have placed the model in the “cone of light” that descends from this window, so the light hits “the face first, then down from there”.
• I have exposed well.
• I have positioned the model to take advantage of that light in the way it lights up her face.
• The background is fairly simple (I cropped very carefully while taking this picture).
• The opposite side is light enough (sometimes you need a reflector to achieve this).

Shots like this can really work. And they are easy – all you need is a window as described; a suitable lens; and away you go. remember tho use a high enough ISO so your picture is not shaky.

Of course you can mimic this effect with flash – and I often do – but do try to also use available windo light sometimes!