Galico, A "tight" cassette is one that the gears have a smaller differance between. Shifting up one gear will require a little more effort. A looser cassette has a bigger jump between gears. Out on the road you can sometimes get at a speed where one gear is just a little too hard to push, but the next one down makes you spin too fast. A tight cassette helps eliminate this.
Cross chaining. According to Shimano, with a triple, you can use the following:
Big chain ring - all gears except the largest.
Middle chain ring - all gears
Small chain ring - a gears excpt the smallest.
Here is something from another thread:
http://www.bikeforums.net/showthread...ange+gear+inch
The idea of three chain rings up front is to give you three different speed RANGES. It is not intended to give you 27 seperate sequential gears. Lots of people on this forum calculate all of the gear - inch ratios and shift a million times trying to shift up and down through all of the gears. That is not how it was designed to work. You generally select a range (Hi, med or low) with the front chain rings. Then you have the gears on the rear to move up and down in within that range.
Looking at the chart above and trying to shift sequentially you would go, 32/23, 44/30, 22/14, 32/20, 44/26, 32/18, 44/23, and 32/16. This is nonsense. You would simply stay on the middle chainring and use the rear cogs and go 32/23, 32/20, 32/18, 32/16. A nice speed RANGE which your legs can handle. (Khuon, I know YOU weren't saying to do this. But some people here think that is the way to do it. I am just trying to show that if you think "3 speed ranges" instead of "27 gears", the gears are not very complicated. And, you don't need to shift a million times.)
This gives you, eight gears in low range, nine gears in the middle range, and eight gears in the high range.