Thread: Routing - Differences between selecting different options in 'Activity for Route Calculation'?

Further to my question yesterday regarding the difference in route calculation between selecting 'Minimise Time' v. 'Minimise Distance' when setting up a Route (thread now Moved to Tutorials section) I found the answer so helpful in my understanding that I now would like to ask if someone could clarify the different route calculations which might be achieved by selecting a different 'Activity'; as this is the next stage in my bafflement.

Due to my lack of understanding I have actually only been using my Oregon for the purpose of checking where I am when out on my Mountain Bike; and for analising my 'Total Ascent' and 'Moving Average Speed' etc.

Until now I have never really used the Routing facility as I have never understood it; for example there is a different 'Activity' for Cycling, Tour Cycling, and Mountain Biking; what is going to be different about the Route Calculations? ..... and considering the places I go on my Mountain Bike why would that be different than a 'Pedestrian Walking' or 'Hiking' or indeed ATV/Off Road Driving? ...... furthermore and what difference for example might there be between 'Automobile Driving' and Mortorcycle Driving'? Help!

For clarity, apart from the usual BaseMap I also have 'Garmin City Navigator' and 'Garmin GB Discoverer 150K' on my Oregon. In the case of 'Garmin GB Discoverer 150K' this does appear to be Routable on the roads? (I guess) but not in respect of Bridelways or footpaths? ... and Byways??? ...... so again how is a calculation for 'Mountain Biking' going to be different to 'Hiking etc. etc?; and 'Mountaineering' ....well I can only wonder!

So that we don't have to get out our Garmins to remember the options I list them below:-

Direct Routing (obvious)
Automobile Driving
Mortorcycle Driving
Cycling
Tour Cycling
Mountain Biking
Pedestrian Walking
Hiking
Mountaineering
ATV/Off Road Driving

I realise that this is a very basic question but it baffles me and stops me from getting the most out of my device, so any help in undestanding will me most appreciated. Thanks.