1. When doing a long distance event I enter the grid reference of each top into my GPS and when I get near I switch the device on occasionaly just to make sure I am heading for the right summit. All navigation is left to map and compass. That is what I did recently when soloing the Cairngorm munros on spec, in bad visibility.
2. Again, when navigating in poor visibility (eg in the night) in a difficult area through fields with stiles etc, I try to reccie those difficult bits beforehand with the GPS switched on. I then follow the GPS crumb trail on the day. I never pre-enter a track from the map as this can be so inacurete as to be useless in a tricky area in the dark. I applied this successfully when doing the South wales traverse last March going through a forest and descending through wooded fields during the night.
3. Don't use GPS for navigation, it is useless when you stop.
4. I use a Garmin, marine version, not a wrist type.
Yiannis