This is what I have read about synthetic vs dino oil is:
1) Synthetic oil does not break down over time. Thus no need to change every 3 months even if the car is not driven like dino oil.
2) Synthetic oil does not break down due to heat nearly as quickly. Thus no need to change due to extended mileage in contrast to dino oil which breaks down due to engine heat.
However:
3) Both types of oil still get just as dirty due to driving conditions. At a minimum, the filter must be changed at vehicle manufacturer intervals.
4) Oil levels should still be verified on a regular basis due to the tiny amounts of oils that even a perfectly tuned engine will burn, or worse yet, due to an oil leak.
The pros of synthetic oils of dino oils are:
a) An engine is under greatest stress during these times (a) when starting the engine (b) when accelerating (c) when idling (d) when driving in extreme heat (e) when under load due to cargo or towing or hills. These forms of stress cause additional heat. The least amount of stress is when a car is cruising along in its highest gear at constant load (ie no acceleration, no hills) since the engine is able to stay cooler due to able air flow through the radiator. When regular oil no longer protects the engine as it has been designed to due heat exposure, the engine would not get optimal lubrication when oil is nearing its lifespan. The problem is that the lifespan can vary tremendously due to driving habits. For example, a car that has been driven for 3000 miles in "city driving" defined as: "(i)Roads that had had stop lights, (ii)stop signs, (iii)stop and go traffic,(iv) or having done many small trips requiring starting and restarting the engine" or (v) during environmental conditions that had high outdoor temperatures, or under increased load such as cargo, towing or hills, then the oil in this car would be in much worse shape than a car that did the same 3000 miles in "Highway driving" with the same dino oil but driven on flat roads with few stops and starts, and few restarts of the engine.
The problem is that you never really know when the oil has exceeded its lifespan. The oil change interval suggested by the manufacturer for regular dino oil is an average of all driving conditions.
This issue is not as great a concern with synthetic oil.
b) As dino oil starts to break down, it begins to contain a little water moisture. In extreme cold conditions, used dino oil does not protect the engine against freezing as well as synthetic oil, since the synthetic oil would not have broken down. Its is a fact that in temperatures below -22F (-30C) dino oil with approx. 3000 miles of wear is at risk of freezing, thus making it impossible for the starter to turn the engine over fast enough to engage. This is why engine block heaters were invented.
This issue is not as great a concern with synthetic oil.
The bottom line is synthetic provides consistently reliable protection. However, it still gets dirty. Personally,I prefer to change the synthetic oil at the recommended interval since its almost as much work to just change the filter, and this way I know I have clean AND reliable oil.
Very nice summary,,, I would like to add the word synthetic can be put on anything,,, YES,,, anything,,, The basics for oil is there is Petro oil base stock III ( mobil 1) and there is PAO base stock,, (Amsoil, Mobil1 extended performance). There are filters designed for 15k plus miles if used with PAO.
I use AMSOIL 0w30 with their EA0 filter,,, this for me after many years of research (no not continuely). I change oil 12-15 k miles BUT I have sent to the lab many samples of oil from various cars I own. Normal base III stock New oil Mobil1 has a 7-9 TBN (a basic wear number, there is many more parameters) AMSOIL New TBN is 13, mine after 12k miles and lab analysis is 6-8 TBN,,, so basicly my oil is just as good after 12k miles as new Mobil1.
I keep all my cars 250k miles plus, I know I can go many more miles before I change oil but I double down on all recommended maintenance,,, It's just me,,,
note I do sell AMSOIL to my friends,,, BUT I don't make any money at it,, IT's just a hobby,,,
I don't want to start a oil war here,,, many people have gone 200k miles by changing oil every 5 k miles,,,

D