revising the budget

Is it true that budgets are revised due to change in the current prices or costs which will force us to revise our budget using current prices or costs to fully reflect the current figures. Otherwise, the outdated budget might not be useful because it has figures that do not reflect the true picture and the budgeting would be meaningless.

Revising the budget means revising the fixed original budget which could be due to inflation, changes in labor rates, changes in material costs, changes in the demand, changes in the production volume, changes in sales price, changes in product, changes in taste/fashion and more?

Please say if there is anything missing.