That depends on the tweaks you need to do.

And, really, you shouldn't have to render anything - this is photoshop. Layers and non-destructive effects are your friend.

Back up your original first!!

I'm a color person, but there are people who "see" tones better than color values. Once in a while I come across an image I think might look better in black and white and what I usually do is first generate the three (RGB) channel images just to see what kinds of values I'm working with. sometimes I simply desaturate to see what that looks like.

Almost every tweak you make is going to result in information loss...

I no longer use Photoshop for BW coversions, I use Lightroom. There are so many options, so many settings & presets that it doesn't make sense to do it in PS anymore. You can dial in the exact contrast, sharpness, clarity, shadow detail, hilites, etc and its not destructive. You can come back to it a year later and change everything or even take off the conversion and make it color again.

It all depends on what you are doing with the image, if you are going to manipulating the image, making clipping paths, etc, I would do that before going b&w. It can be easier (depending on the image) to do work of that nature while still in color. You have more selection options.

If you have CS3, there is a new adjustment layer for making an image greyscale. Pre-CS3 I used to use the lab conversion 90% of the time, it doesn't work well with images that have a lot of red (translates to 50% grey). I would use the channel mixer for those images. Now that i have CS3, the Black & White adjustment layer ROCKS!!! You can apply a "filter" to add contrast similar to adding filters to your camera lense. I tend to use the green filter for most images. It works beautifully and is non-destructive. You can make custom "filters". I merge the layers holding down the option key to make sure, it does not flatten, i save the .pds, then convert to greyscale and save as a tiff.

I highly recommend CS3 for that feature. Huge time saver and works brilliantly.

I, sometimes make adjustments after the black & white layer if nec. There is no "black & white" answer to your question... it all depends on the image and what you want the end result to be...

4.5min video tutorial:
www.adobe.com/designcente...vertbw.html#