Why does a compost heap have holes in the side and at the bottom?

A compost heap has no lid. But compost containers such as bins indeed have lids. The cover makes it possible for compostable materials to contain smells, discourage unwanted micro-organisms, hide from foraging wildlife, keep low profiles in clean neighborhoods, maintain proper environmental conditions (of light, moisture, temperature), and resist dispersal by winds. It permits composting to take place in shorter composting times since layer-turning takes place in more confined spaces.