Len's Hood are supposed to prevent your pictures from having flare from the direct sunlight..
Usually a lens hood are essential for outdoor day shoot.. Indoors and at night a lens hood won't be necessary..
...not to mention it ups your 'pro factor' by a notch.
A hood, after all, is an accessory. That means your lens will work fine with or without the hood on. Mainly I use the hood more for protection - how often do you shoot with a strong light source, and how effectively is it really?
Aye, the purpose of me using a hood is the looks factor, in fact if the front element doesn't rotate, and the supplied or optional original hood is a barrel hood, I'll try to shop for a cool looking 3rd party design hood to screw on instead.
Secondary purpose is to avoid a kid from sticking a finger in... or other things from happening to your lens.
Glare is usually the last of my concerns, if you know how to avoid it, it shouldn't show up... then again, my hood is always on when I shoot. I even have hoods for my kit lens =) (just don't buy the original hoods all the time, its way over-priced).
Lastly, I just feel 'not correct' without a hood. The front (filter or not) with the hood threads exposed just looks a little wrong, and doesn't feel safe. But thats personal too. So yea, you decide if you need it. All in all, its not an essential, but very good to have. Afterall you paid a hefty sum for your lens.
I've never believed in round or petal hoods. Just doesn't make sense considering the format we're using (rectangle). But during most applications, they're faster/more convenient than bellows hoods.
Look at the most exacting and demanding capturing applications - cinematography. ALL their lenses are hooded with a deep or adjustable rectangle lens hood.
Also bear in mind that most manufacturers design their lens hoods conservatively - often, so conservative that it's ineffective. As an example, I can easily use a 85mm setting on my Bronica bellows hood on a 24mm lens on a 1.6x crop body, shoot at f/11 and get no vignetting.
Just to add on a qn. Is it more advisable to buy a lens hood before I get to Japan since it's winter, I heard the snow glare is quite strong. And should I get the *polarised* filter too? *paiseh forgot the filter name. hehe
I considered getting the RB hood as well, but it's so heavy!
I wonder if the Lee or Lindahl is made of plastics or ploycarbs? Anyways, search ebay - sometimes you can get the Mamiya hoods around or less than US$100. I once missed a deal for an RB hood and it went for less than US$70.