if you are right handed why would you lead punch with your non dominant hand
because you want to give your dominant hand the chance of express it's max power (rear hand) while the weaker one is keep lead to create interference and openings
It depent also in body built, style etc
Example i'm usually at height/range disadvantage with peoples of my weight, so i'm not going to engage jab wars or rely on the cumulative damage of fast lead punches, i've to find ways to get in close and when finally you do it you want your strong hand to be fully charged to pay back the fucking giraffe that made jabs rain on you lol
Also when you clash close, your lead hand end up suffocated by opponent's lead arm or body... got a friend who's better boxer than me and stay southpaw with his strong hand leading, but if you trap/block his right arm action just by keeping very short distance all he got are bitch punches with his rear weaker hand and get owned round after round
lead= faster, used more often, better range, get A LOT more chances
rear= more power, harder to trap, works good in close distance scrap, get tired later
One side is annoying knowing you're giving your better punch less chances of play but on the other you're keeping it for best chances
Again, it's about preference and style, and likely these should be influenced by your build/qualities
Btw as general thing i ever thought that "dominant hand" is'nt much a dramatic thing once you train a lot your weak one to do it's job... if i try to southpaw i don't feel i've a stronger lead game, i feel it's more powerful but not as fast and precise as when i let the weak hand to do it.
Also i notice trying southpaw i lose combos mindset, starting from 1-2s lol, as usually the idea is quick stab with the left and follow with an harder shot of your rear strong right