I have a Nikon d200, when shooting outside on day, shall I use flash?

I have a Nikon d200, when shooting outside on day, shall I use flash?

If you need the flash fill, sure.

Just be sure that your shutter speed is not faster than 1/250th second, the flash sync speed of your fine D200

Hmm…
I don't think it's necessary.
I don't like pictures with flash, so i never use it: P

If it is high noon and your subject has raccoon eyes, if you are in mottled light, if your subjects back is to the sun, then by all means, use a flash to fill in the light.

If you want to or need to then do so.

That is entirely upto you and what you are shooting and the effect you may need whether you use flash or not.

I believe these articles will answer your question:

http://www.shutterbug.net/techniques/portraiture/0710portrait/index.html

http://www.shutterbug.net/techniques/pro_techniques/1007fillight/index.html

Since both articles were written by professional photographers they should convince you that using your flash for outdoor portraits is a valuable skill to learn.