It is good financial planning to regularly review your budget including all your spending.
This sort of review will not only allow you to monitor your spending in line with your budget but it will also highlight any irregularities in the use of your bank account or credit cards. Early detection is key to stopping any fraudulent use of your money or to spot instances when you may have inadvertently 'signed up' to subscriptions you don't want.
you took advantage of a promotional offer over Christmas and new year, you could get a nasty surprise when you next check your bank statement. Angry consumers have told The Times about payments deducted from their accounts when they say it was not clear they had given companies permission to set up a direct debit.