@Noman, it all depends on the actual gear ratios and transfer case ratios. Obviously, you roughly get 1.9 to 2.5 times more torque (depending on transfer case ratio) but your speed is limited. It is unlikely that you will get similar speed in 2nd Low vs High 1st, i.e you will be able to go much faster in high 1st (in most transmissions, the 2nd gear ratio is roughly 60% compared to 1st). Now, obviously, if you are bogging down because your vehiclel doesn't have enough power to push through sand in high ratios, i.e you lose engine rpm and hence power and eventually torque, than low gears give you additional required thrust / push.
Like Sajid, I also had a chance to try low ratio run for some distance during recent Cholistan Rally. It felt so much quicker and responsive in slow sections, but as our top speed was limited (because of gearing to max 105km in topgear at red line) it wasn't helpful during the rally as there were plenty straights, on some of which I managed speeds over 145kmph, while some others were going much much faster!! Now, that obviously can only be ahieved in high ratios.
Bottom line, you drive in a gear/s your vehicle engine response feels most appropriate for the speed you want to maintain/ achieve.