In the natural gas business, we use teflon tape on all threaded
connections where we don't want gas to escape, which is all of them,
including the installation of sensitive devices. Of course, as
mentioned earlier, we don't use it on compression or flared
connections.
Teflon tape has to be used properly, or the chances of little bits
getting into a myriad of orifices, causing upsets and failures, are
very good.  I believe that is the only reason you are discouraged from
using it in a Propane application, i.e. because, unless you've had
instruction and practice, you are likely to apply it incorrectly, and
it will leak, or come apart inside your system, or both.
Miguel