What do you consider when deciding to use a high-efficacy DMT as an initial treatment in multiple sclerosis?  

I'd say the question is when would you "not" consider a high-efficacy DMT in MS. High-efficacy therapies (specifically, B-cell depleting therapies) have a good risk profile and are exceptionally effective in treating relapsing MS. Evidence would suggest that you get the largest "bang for your buck" ...