In Magento if we want to call function from model then we prefer to use Mage::getModel('moduleName/className')->functionName(); but we can also achieve it directly using Namespace_ModuleName_Model_ClassName::FunctionName();
I know as per Magento we have to use getModel but I checked someone used direct Php method to call function and said "This was preferred against the Mage::getModel way due to the fact that we won’t need to instantiate the whole model for one simple array. If we would use the Mage::getModel expression, the model will first need to instantiate (executing its constructor) before executing the “functionname” method, which only returns an array and does not have complex logic. This way it’s way faster and it also limit the logic executed to return the steps array."
Please suggest which will be the preferable way to use and advantage/disadvantage of using direct calling function.