Preventing oxidation is the real reason to transfer, if I'm not mistaken. You want to transfer while there is still a little activity to blanket the wine in the carboy.
Luc, do you start your ferment under airlock? Some people do and that is why they can get away with waiting for it to go dry. I have mine in an open, cloth covered primary. As soon as the big foaming is done and I'm sure I won't have an eruption in the airlocked carboy... I transfer. Sometimes it gets away from me and it is dry... but usually it's 1.020-1.000.
I don't want the poster to get confused between racking off the primary, and removing the fruit. Some fruit, such as Elderberry, needs to be removed from the primary, but not necessarily racked to secondary. The tannin is indeed very high in Elderberry. Other fruits, such as blackberries, raspberries, strawberries, etc, have seeds which cause BITTERNESS, and it's best to get them out in 3-5 days. These decisions can be personal flavor preferences and difficult to put an exact time line on. Some wines take 3 days and some 14 days or more to finsh dry, so you'll take the fruit out, but let it continue in the primary. This can be due to temperatures, type of yeast or other factors.
I hope this helps to clarify, just a bit!
Good Luck!
Debbie