I have been considering to buy a mini video beam for my work. I have been studying several machines and now the prices may be really affordable. But I haven't been able to play any games using one of those. Putting aside the fact that you will need a really dark room (which in my case won't be a problem) I really don't see the difference... But I really don't know (that's why I am asking)

So is it worth it? What would be the advantages and disadvantages of gaming using a video beam? (A video projector)

A video beam?   Do you mean a projector?

Yes, I mean a projector

Lower quality, in general (primary due to light reflecting off dust, in the proximate atmosphere), other objects can also interfere with the projection, people walking across and whatnot, so this effects placement. The best place to have them is on the ceiling, usually. Image takes the attributes of it's surface, which isn't an issue if you have one of them board thingies, they don't have any built in sound that I know of so you will need a set of speakers to output sound.

Generally though the image looks lesser in quality, over all. With reduces colour fidelity, and looking slightly more washed out, but still great if you have a good place to set it up, and a good projector. Honestly if you can get a setup like that isn't intrusive, it's probably the best way to go. (like if you want a gaming (exclusive) room). 

By the way, I just noticed your name. If you're intending to do it to a Wii. Do not, stretching the image out like that will make it look real garbage. 

I've played wii on a projector, and it is a HUGE pain in the ass.  we had a gamer day in the anime club I attend, and the sensor bar was a pain almost the entire time.  as stated above the picture also looks inferior to a TV.  How much are you willing to spend on the projector?, that would make a huge difference.

Not good, i played with my old friends with it , and you really can't see anything if you move a little bit! let alone even when straight you can barley see, but we had a laugh and all, it was a marathon game night where we play a whole game from start to finish , and that night it was Rise Of the Kasai on PS2 and the night after that was RE4 on Gamecube... good ol high school times

Edit : Tv is obviously a better choice and i think it will be better for space , time and money you are going to spend on that projector.

Seems some ppl have made bad experiences ...

I use sometimes the beamer (projector) on my workingplace for wii gaming sessions with co-workers. (Of course after the work is done ...) The picture is bigger and I think it's better suited for local multiplayer with motion controll than a TV. However the light can really be a problem. Playing dark games with a projector is not recommended. Usually I play games like Wii Sports, Wii Sports Resort, NSMB Wii, Mariokart, Boom Blox, Wario Ware or Metal Slug Anthology with my co-workers. All are games, were the graphics really don't matter and all have bright graphics. Oh and placing the sensor bar might be a little bit tricky, but it is doable. A wireless sensorbar should be a great help.

However, for normal single player or online multiplayer gameplay I would use a TV.

PS: My brother has an HD-beamer, which seems to be better quality than the ones we have at work. However I havn't tried it with my Wii.