Below I'll outline a few reasons why and when you might need to review your campaigns.
The season requires it
If you are a retailer or your business is affected by the holidays or summer season, it is important to review your marketing data pain consumer email list around those dates. I suggest you create open and close dates for each season. These dates mark the beginning and end of each marketing cycle. During a cycle, your marketing is running in every direction, and on rare occasions, you should not change things within those dates. The idea is to create a plan, execute it, and then review the results to improve. If you try to make changes while executing a plan, it will be a little difficult to pinpoint exactly what made that plan actually work. Be patient and try to create plans that you can execute from start to finish. If you are new to email marketing, start with small campaigns of one to two emails and then expand to more as you learn.

When planning around a season, I suggest you make plans at least one to three months before it starts (depending on the size of the company and the people involved, as larger companies need more time). Don't plan too far in advance.
When reviewing your email campaigns after the campaign closes, it is very important to look for improvements to apply when a new seasonal campaign arrives.
Important changes within your company
Let's say you've just added a new product or service. This is the perfect time to review your marketing data. You want to make sure that this new product/service is front and center. If you're in the middle of an existing cycle that's being executed, you can just throw it in an email announcing your new product or service and then figure out how to incorporate it into your ongoing marketing strategy later.