I would be very careful about capturing the GS prior to being very sure where you are ... following on from BOAC's comments, consider two f'instances
(a) gave an experienced crew a routine approach with crew navigation. They were running normal autoflight control. For whatever reason (we were assured after that the sim wasn't programmed to capture false LOC) the box turned in on a false LOC and commenced descent on the GS.
The crew lost SA and, had the incident being in flight rather than the box .. would have been unpleasant ...
(b) have a read about the Air NZ Apia 767 false GS capture .. was about 4-5 years ago as I recall.
There's a great deal to be said for being procedurally rigorous when the aircraft is near to the bumpy bits ...