Polarizer filter question(s)

This is kind of a multipart question.

I am contemplating getting a polarizing filter for use with my 4x5 setup. I shoot only black and white. Is it likely that a polarizing filter would become an important part of my photography, when shooting black and white? I know that many use it for color saturation in color photography. Also, I have read that the filter gives me aprox. 2 stop less light. When applying this to a moderately slow lens, I am assuming that viewing the image on the ground glass will be difficult. However, isn't it important that I see a pretty clear image on my ground glass to determine the proper adjustment of the filter, to properly polarize the light? Lastly, is it safe to critically focus on the ground glass before applying the filter to the lens?

Thanks!!

If you shoot only black and white, wouldn't some colored filters--red, yellow, green, etc.--be more useful than a polarizer? Indeed losing two stops will make it difficult (although not impossible to focus) on the ground glass. Since colored filters need no adjustment (just compensation in exposure) you can compose, make camera movements and focus before you put them on. Actually you can do the same thing with a polarizer if you put it on and adjust it after you compose and focus. If you just want to deepen the color of the sky, or lighten up foliage consider one of the colored filters. If your main purpose is to control or even remove reflections from water, or other shiny surfaces, a polarizer would be a useful filter for black and white.

I shoot 4x5 using black and white materials almost exclusively. I use a polariser a lot and don't find it hard at all to focus with it on the lens. I can also align it before hand and then put it on the lens carefully. Yes if all you want to do is change the tonal relationship of certain items within the scene then I would use a colored filter but to take off flare or glare from things like leaves, glass, change the tone of the sky, I would use a polariser. And I have slow lenses but still have little trouble using a polariser on the lens as I focus the scene. There's a trick to it but I'll let you figure it out. A hint though. Light rays travel in straight lines.

I use both a polarizer and color filters, mostly orange and green, occasionally red, almost never yellow. When your only purpose is to darken the sky a polarizer is nice because it doesn't have a major effect on the tone of other things in the scene, unlike orange and especially red filters which can make green foliage turn black. OTOH, the light source has to be at the correct angle in order for a polarizer to be effective so sometimes an orange or red filter is the only choice. And as someone else mentioned, a polarizer is very nice for removing reflections from things like foliage and water. You don't always have to use the polarizer for its maximum effect. For example, to me water doesn't look realistic without any reflections at all so I use the polarizer just part way with water, to minimize but not completely eliminate reflections. I think there's plenty of room for both colored filters and polarizers, I wouldn't want to have to choose only one or the other. Each can do things the other can't.

I usually compose and focus without the filter (polarizer or color), then put the filter on and recheck focus (and adjust the polarizer when using it). Rarely if ever do I actually change the focus after putting the filter on, doing it just makes me think I'm being careful and methodical like a proper large format photographer is supposed to be. : - )