When you’re running into a headwind, drafting behind another runner is beneficial, as it lessens energy cost by reducing air resistance. However, when it’s calm, it only really has an effect if you’re running faster than 7:00min/mile.
You have to be close behind to get an advantage – more than one metre and any help is significantly reduced. This is also true if you’re not directly behind. Runners also find drafting behind a runner helps them relax, as they don’t have to focus on their own pace. There aren’t rules to prohibit drafting, but it may be seen as unsporting if you stay close behind someone for many miles in a road race. In general, it’s nice to share the pacesetting with others.