Often recipes say to chop garlic, but I usually cheat and just crush it as it's quicker. Is there any difference in doing this? Will it have much of an effect on the flavour of the dish? 
I guess it depends upon the definition of "crushed" If by crushed, you mean using a garlic press, then there is quite a difference between chopped and crushed garlic. When you crush garlic, no need for a garlic press, the flat of a knife and a little salt is all that's needed, you release the essential oils, resulting in a stronger flavour. You can also purée the garlic.   It's also important to consider the type of recipe, in some recipes, such as a pasta sauce, chopped garlic is fine. In Asian cooking, especially Indian cuisine, it's common practice to use minced or puréed garlic. In roast dishes, using the whole cloves in the roasting tin with the meat, can produce an incredible sauce. 