I find that having 1 mile laps is useful and do not understand why it was never a default setting as it seems to have become one on later watches.
How to create 1 mile/km or custom laps on your Garmin Forerunner 305:
Press Mode > Training > Training Options > Auto Lap > Auto Lap Trigger (Set this to ON)
Lap at (Set this to 1 mile or 1 Km or there is also a custom setting)
Press Mode to come all the way out
There is more information here: