A automatic you want to put it in low 1 and you can shift up accordingly. Reason for this is to apply the low/reverse band to the drum ( this is what provides engine braking in low gear and protects the sprag from any shock, hooking up on dry pavement having to suddenly let off gas, etc. Any violent or abrupt drive line breakage the trans should be pulled and sprag inspected for jammed or stuck rollers (these are what locks the sprag and causes the forward drum to spin 2.2 times engine rpm and at 9500+ it usually comes apart, like 4100 rpm is enough to get into the danger zone)
In a automatic in drive the low/reverse band is relaxed the car can go either way when you give it gas, what always makes it go forward is the overrunning or one way clutch. If you ever had the car in the air in neutral and turned the driveshaft one way is pretty easy one is definitely harder, well that is the overrunning clutch making sure you go forward in low gear without the band applied, this is done to get a faster easier shift into second gear under normal conditions.
A manual reverse valve body (old style ones anyway) use the fact that there is no low band applied in drive/low and get manual control without the low band apply, this is why you never do a burnout in a manual reverse valve body car in low gear, always use second gear it protects the overrunning clutch. Using that strict instructions that come with every manual valve body I have ever bought, leads to the USE LOW 1 TO DO BURNOUTS IN A AUTOMATIC TRANS, protect your overrunning clutch/sprag. I believe it is a good idea if loaded heavy(pick up truck) or towing heavy and in stop and go rush hour type traffic I would keep vehicle in low gear to keep from on and off the rollers in sprag. Just a thought
