Can you give a link to the Microsoft website where I can read this recommendation? I might get other tips there!
All this accomplishes is a calibration for the percentage shown. Most lithium-ion batteries have fairly flat discharge profiles so it can be hard to estimate percentage based on the voltage. By doing a full discharge it can accurately display the percentage later.
You will get the most usage out of the battery by doing the shallowest discharges you can, but that's not entirely practical. A 50% discharge will give you the most practical use. In reality, though, you don't need to worry about it. Leave it plugged in when the battery is full (most likely it powers the surface directly from the charger, rather than the battery at that point) and discharge it as much as you please when you use it away from the wall. Normal usage for most people puts the battery life at around 2 years before you get down to around 80% of original capacity. What will damage the battery most is heat, so don't let your Surface sit in a hot car or anything. You may also notice that if you use it in very cold environments that you get less use out of it, but it's not really a realistic case and it shouldn't permanently damage the battery like high temperatures do.