What are the pros and cons of budgeting and forecasting

A budget is (usually) an exercise to create the initial, static, expected financial results for the time period, usually the 12 month fiscal year.

A financial forcast is performed post budget and takes into account the actal results, changes that have taken place in the static budget and any new items not budgeted. The forecast can be for the balance of the fiscal year, or go out beyond the budget perod (i.e. rolling 12 month forecast)