Adequate lubrication allows smooth continuous operation of equipment, with only mild wear, and without excessive stresses or seizures at bearings. When lubrication breaks down, metal or other components can rub destructively over each other, causing destructive damage, heat, and premature avoidable failure. The right lubricant will keep your bike working properly for much longer and will save you a heap of money in the long run. You'll need a thin, dry lube for the cables and pivots of your brakes and gears. This will resist water and won't attract dirt. Chains require something heavier and will use different lubes for the different seasons. In the summer, a White Lightning type lube will keep them clean and protected but wetter weather means you'll need a more tenacious alternative.