Im struggling with understanding when I should be using time series vs a single time aggregated period cross sectional.
Say I have many customers and i want to understand the impact of marketing on sales for a single year (say 2020). I have daily sales for each customer as well as marketing events that have happened throughout the year for each customer. I also have individual non-time varying variables for each customer.
One option is to do something like a two way panel regression looking at monthly sales data per customer as well as monthly marketing. You would likely have to take into account something like adstock (which is common in marketing analysis). Other considerations would also need to account for autocorrelation and the like as well.
Another way is using the total marketing promotion for the whole year compared to the difference in sales for a given customer (2020 vs 2019). This is a single model to see if customers with more marketing events had a higher change in sales compared to the previous year.
Is there a reason why i would want to use a panel regression / time series model over the aggregate for the given year? Is the aggregation method incorrect?