Probate is the process of verifying that your will is legal and that your final wishes are carried out. A will does not help your estate avoid probate. It simply makes the process smoother because the court can use it as a guide to what you wanted.
For most small estates, probate is a pretty simple process that can be completed relatively quickly. However, things may slow down if someone contests your will, which means they challenge what’s in it. Perhaps they feel they were wrongfully excluded or that they deserve something other than what the will says they'll receive. Contesting a will can drag out the probate process for months and potentially cost a lot in lawyer or court fees.
If you don’t have a will, your estate still goes through a probate court. The difference is that a judge will appoint someone to handle disbursing your assets.