Up Side: don't need a loader, so you can either carry more rounds or make the tank smaller Down side: They break One less crew member to crack tracks Note: they work 99% of the time ? There is NOTHING on a tank that works 99% of the time There is no military equipment made, that works 99% of the time
Auto loaders are complicated pieces of machinery that don't always work. Usually the tank crew works on their own tanks in the field and that's one less guy to help maintain more machinery.