I have a strong preference for 3 leg sections on gitzos (e.g. 1329). I do mostly nature
shooting (botanicals and landscapes). I'm often opening the tripod, shooting a
bit, and closing (or partially closing). So, 3 sections is as much as I'm willing to tolerate.
I'm not sure that 3 sections is that much more stable than 4. The tradeoff of 3 vs 4 is
really speed vs. packing length. Of course, 3 section tripods are a bit longer when packed.
This also means that the minimum height of the tripod (legs collapsed) is higher.
By the way, before using gitzo's I used to use benbo tripods which typically have
2 leg sections. The lower section is also the outer (sealed) tube, which is a great
design feature if you ever have to immerse the legs. Benbos are much better for speed.
I stopped using them, however, because the welds and the splines didn't hold up
over time. Nor did they make a carbon fiber unit (as of a few years ago).
With the same loads and fairly heavy use (i.e. nikon d2x, pentax medium format, and
contax medium format), i've never had a structural problem with a gitzo.
On the other hand, if you put a gitzo in sandy water so that the collar is immersed (i did this
once not realizing the problem i was creating), you have to fully disassemble the
legs to clean the sand out.