While it's true some shots are best gotten outside the fence, but the best (& most) low angle shots are inside. More importantly the trip around the track is shorter..
Plus you have a greater choice of track topography and don't need as much reach.
Here is an example of the credentialed guys shooting the shadowed side of the riders at the best whoops at the Honda Supercross in Daytona. The source of the light was above the grandstand
the best low angles may be from inside the fences...but does not mean they are the best angles. problem with MX shots like the one above it the clutter normally behind them. i'd rather see the track than lights.
the advantages of having credentials is that you have MORE options to play with.
if i were shooting MX i'd would rarely shot from ground level, cuz the track is built up. and if my observation is correct, the photogs can only stand on the outside of the track.
