Well there are two sides of this....
Side 1: Magick that is created completly from scratch with all of your personal attention, creativity and imagination is the most powerful.
Side 2: Magick that has been performed in a similar form repeatedly for years, generations or centuries gains in power due to accumulative use.
Many Wiccan groups completly subscribe to the first side...
Many of the older traditions and belief systems respect the value of side 1, but having seen the power of things used over long periods of time also give respect to side 2.
Neither side is wrong, but I can attest by experience that both are quite viable and powerful. In most cases a nice compromise is very nice and workable as well. The fact is some covens have rituals that are done, such as Initiations, as closely as possible to the exact methods each time. Each initiation grows in power as a result. These rites are kept VERY secret, mainly because if they were common knowledge they would loose a good deal of their potency. To face the Unknown is a major factor in the Initiatory process, so to be able to read the Initiatory rite in a book would detract from that major aspect.
Also, don't forget, the Craft is a "Mystery Tradition", if its all public then it becomes sunday school at the local babtist church. I think its best that secrets be kept, cultivated, created and passed on in the manner they have been since the Temples of the Old Gods were in use. If we all knew how the Oracle of Delphi worked, then much of the spiritual discovery related to the Elusinian Traditions would be lost. To site one example.
Even the devil's got a lawyer, would you like my card?
Est nullum problema tantum ut usu vis maximae idonei expediri non possit.