Cross-sectional research is an observation of all population or a representative and it is at a certain time.when someone is using cross-sectional study they tend to have data on a whole population instead of one specific topic. a longitudal study is when it is repeated observation of the same items over a long period of time. longitudal studies mesure things around life span events and important things that have happened. when you do longitudal studies it makes things are more accurate because you have been looking at or studying the same thing for a long period of time. so this kid of study is reat for the field of medicine because you been looking and going over something for a long time you can tell if it is affective or what works and what does not work. same as medicine you could also use it for advertising to see what shows are getting watched more what actors are becoming more famous or even what restaurants people want to go to. there are many things you can do using the longitudal study and most of it is going to be very accurate. there is also types of longitudal study such as cohort studies and panel studies. when people are trying to choose which one to use most pick longitudal study because they are more accurate and study a certain thing and it gives you a lot more information and the cross-sectional they do need to use sometimes but its does not have as much direct data like the longitudal method does. so i mean it really depends on what are you doing research on and if you want it quick and not bad information or if you want it to take a bit longer and have very accurate information.