Hi Dia, you will probably get about a million responses to your questions so I said to myself "why not, I'll be one of them.":) My answers below are verrrrry brief.
1. Many data warehouses or data marts start out in their infancy as monthly snapshots in time. They typically included summarized (totaled) data, such as total ATM withdrawals, average daily balance, and status codes on an account for the entire previous month. Moving to a weekly or even daily load takes quite a while for IT and database people to set that up and it requires much more storage space for the data.
2. Typically promotions (direct mail drops) occurr a number of weeks beyond the time the mail house gets the data. By that time the data could be 1,2 or even 3 months old. I suggest you send a "purge file" of customers with closed accounts, delinquencies, opt outs, new employees, or those with any other undesirable behavior (and those that have opened an account since the data was pulled) at the last minute so your mail house can remove them from the file. This should be a common practice.
3. When building models you typically need to pull historical data from before the customers opened the accounts, ie., an EquityLine, or did some behavior you're trying to model, like signing up for eStatements. This may require you to go 3 to 4 months back from the current time period. You want the data to reflect the customers as they were before they responded to the promotion. Month-end snapshots would work fine for predictive modeling.
Hope this helps!
Ben