microbio

NAD+ is involved in redox reactions, carries electrons from one reaction to another. NADH (reduce form) acts as reducing agent to donate electrons. These H+ ions that it carries are used to produce adenosine triphosphate (ATP), the main energy intermediate in living organisms, as they move back across the membrane forming an H+ gradient (electrochemical gradient).

The main advantage of converting pyruvate to lactate to convert NADH to NAD+.

This is its sad sad attempt to get some ATP out of the sugar, despite anoxic conditions. If you look earlier in the glycolysis process, you'll see that there's a step where NAD+ gets reduced to NADH, and then an ATP is produced. If the cell runs out of NAD+s, then it won't be able to move on to that ATP-production step! The pyruvate is reduced in order to regenerate the NAD+

Can you please restate you second question