I want to illustrate my question with the following example:
I have a wholesale company through which I sell 200 products:
P1,P2,P3 .... P200
to a 1000 customers C1,C2,C3 ... C1000
I keep my sales records in a database as a time series in which I keep the
product_id,customer_id, amount and timestamp for each transaction over a period of 4 years.
My question is regardless of the forecasting algorithm (static or learning), can predicting the sales of all of these products made through a single model? or model for each product, or a model for each customer? If any or many of these choices can be valid why ?