I am a beginner in the field of the tripods and among the manifold varieties of products I would want to establish some firm points based on the real use on the field:
1) is the rapid column really useful or you almost never use it?
2) is to prefer a tripod with 3 sections legs for the greatest stability and the most rapid setup or the 4 sections for the greater portability?
Every help is appreciated and useful to clarify my very confused ideas.
Your best bet would be to post this in the "General Gear" board - that's where the tripod freaks hang out
Since you posted this in the Wedding board, I'll assume you want a tripod for weddings and answer based on that.
1) I frequently use my rapid column for weddings during the formals. This also happens to be (more or less) the only time I use a tripod, but when there's a quick height variation (say the groom and his brothers are all 185cm, and then immediately after I shoot the bride and her sisters, all of whom are 165 cm) it's helpful. You don't necessarily need a long rapid column - one of my tripods has a 45cm column, the other has a ~20cm column, which is plenty long enough)
2) I like 3-section tripods - how often do you need an extremely portable tripod at weddings? Unless you're a big destination shooter and fly all over, so it needs to be fold up very compact, I'd stick with a 3-section unit. Simpler, less moving parts, and lighter.
Yes I refer to the reality use during a marriage.
For example also when is wanted to make a shot above the crowd of the guests, it is worthwhile to use the rapid column instead of modifying the height of the legs (rapidity instead of the stability)?
My tripod goes to about 198cm (6'6" for the gringos) but that's usually not tall enough to shoot from above. You want to be 2.2m at the minimum to get the effect from shooting up high. Something like 2.5m would be ideal for shooting larger groups.