Operons are often described using all or nothing language. A repressor binding to the operator is usually presented as "turning off" the regulated genes. Case in point, Scitable at Nature.com says:
In addition to being physically close in the genome, these genes are regulated such that they are all turned on or off together. ... The ability to turn ... genes on or off as a group therefore provides an efficient way to quickly adapt to environmental changes. ... mutations affecting the promoter can prevent all of the operon's genes from being expressed, ...
The thing that confuses me is that I've also heard genetics aren't all or nothing, that genes can only be "down regulated" or "up regulated", not truly turned on and off.
Obviously, differing amounts of moderate levels of whatever effector is modulating the repressor could lead to different levels of downstream expression. But, what about situations where nothing is inactivating the repressors? Will the regulated genes be (for all intents and purposes) be turned off? Additionally (and relatedly), is it even a realistic scenario for an operator to always (or almost always) be bound to by such a repressor?