Sjakie,
The scenario that forget describes is the one you'll be most likely to come across operationally. However, untill a fault is detected by ATC on either LOC or GS, you may very well recieve a correct ident.
The ident goes with the LOC only (and DME if paired) - so even though you have correctly identified the facility, you have no guarantee that the GS signal is valid. That is but one of the many reasons we do a GS check after capture.
The GS gives very intuitive guidance, and it's very easy to rely on it completely. Try doing a search for "NZ60" and see what comes up. The video reconstruction gives a quick lesson in airmanship, both how it can fail, but also how it's used to break the error chain. Lore has it that it was ultimately a GPWS warning that saved the day, but that - as most things here - is merely speculation and rumour
. Either way, all lived to tell the tale, and we're all wiser for it.
Oh, run a quick serach on "Murphy" whil you're at it
