Proper saddle positioning is critical for comfort and performance, and dialing it in perfectly is often a process of trial and error. While many people can find comfort with their saddle positioned perfectly flat and in the middle of the rails, others may need to shift the angle, height, and fore-aft position to optimize it for their body or riding style.
Saddle height is generally fairly straightforward and is necessary to achieve proper leg extension during the pedal stroke. Sliding the saddle fore and aft on the rails can lengthen and shorten your reach to the handlebar. Adjusting the tilt angle of the saddle can help to optimize its position for the right amount of support for your body position while riding. When in doubt, consulting with a skilled bike fitter is a great option to get your bike dialed in.