One of the biggest mistakes I made when I was first starting a compost pile was thinking smaller is better. I chopped up everything I put into my compost super small because I thought it would help the move decomposition process along. In truth, there are huge benefits to varying the particle sizes in your compost!
When you put both larger and smaller particle sizes in your pile it strikes a balance between accelerated decomposition (from the smaller particles) and generating structure and oxygen flow (from the larger particles). Eventually, your larger particles will break down and become the smaller particles.
Remember that while size variance is great for compost, you want to avoid putting really large particles in your pile like a full cardboard box or a large tree branch. Particles that large will have a hard time integrating into your pile and will take a long time to decompose.
The right ratio of smaller to larger particles will be unique to each compost and depend on many factors like what is being put into the compost, weather, size of the pile, etc. This means you can play around with what works best for your pile!