One good reason to get the alternator started early on an R1150 on cold days is that the engine idles more smoothly with the battery voltage at about 14 V with the alternator charging than at about 12 V with the alternator offline.
The reason is that when the voltage drops to 12 V with a cold engine, the fueling is Open Loop. At 12 V the injector turn on time is much slower, and although the Motronic tries to compensate, it doesn't compensate enough. As a result the mixture is leaner than optimum and the engine runs less smoothly.
Below is a post I made a couple years ago:
Here's a good example of the alternator coming on late. It was before I figured out what was going on.
Looking at the curve below from 40 seconds to 60 seconds you can see the START-UP enrichment program being run. In that period, the Motronic is gradually reducing the enrichment.
At the 60 mark, until about the 2 minute mark, the Motronic is holding the length of the fuel pulses fairly steady, but it looks as if the mixture is getting richer. This is because as the engine warms up, more of the fuel gets burned and there is less oxygen in the exhaust. And what the O2 sensor is measuring is oxygen which effectively means mixture.
The from the 2 minute mark until about 5:10, the Motronic is gradually reducing the fuel as the engine warms further. But you can see at 3:20, the mixture steps down. This is exactly when my alternator started charging. The injector pulses didn't get longer (in fact they got a little shorter as the Motronic uncompensated for the low voltage) but the Battery Voltage got higher and the injector turn-on time got shorter and they squirted a bit more fuel--roughy 7% more.
Had the alternator been running from the beginning, the first 3:20 of the graph would be shifted down by about 7% richer.
Finally just before 5:20, the Motronic goes Closed Loop and settles on +- 13.8:1, which is where my LC-1 is set, 6% richer than a stock O2 sensor.
Here is a clean start of my R1150RT with everything working as it should on a day when my garage was about 45 degrees, same as above. You can compare it to the previous graph where there is the step down due to the alternator coming on late at 3:20 on that graph.
Because my mixture is richer than standard, the start-up is richer too but it seems to work fine.
