Budgets are the financial targets the company is working towards. They are typically only updated infrequently (once every few months or less). Budgets are set at the account level in Yordex, and only Admin users can update them by importing budgets.
Forecasts are your best guess of actuals. They can change frequently. Forecasts are set at the supplier level in Yordex and all supplier budget owners can update them whenever they want.
We separate budgets from forecasts because you want to keep financial targets fixed (budgets), but still give the business flexibility how to achieve those targets (forecasts). The sum of the forecasts should add up to the budget, but only at the higher levels over the full planning period.