Larry Roeseler? Haven't heard that name in a while...the man's a legend! Lucky for you to have worked with him!
Standing in gnarly dirt situations is easier on your body & also allows the bike to move more freely & fluidly without the riders weight bouncing everywhere. And, yes, it's a skill that isn't always easy for noobs. There is definitely a feeling of security associated with sitting & white knuckling the bars. But once you get the hang of standing up & feeling the bike flow, your riding goes to the next level.
'14 KTM 350 XCF-W
'13 BMW F800GS (low)
'08 Yamaha FJR 1300