How Long to Keep It        
In a recent article concerning "records retention rules" for keeping, and for discarding, business records suggested:
The article included a statement similar to this one, ant if their lawyers think it is needed, far be it from me to argue.
NOTE: We are NOT accountants, nor are we tax advisors.  The comments here are based on information we've received from several sources.  Before you make any decisions, or changes, you must check with your advisors to insure the rules applicable to you are complied with.

Those rules are really directed at "business records", where does the information maintained in WeLoop.SAMS fall?

In the discussion about Commission Accounting there is mention of using the dates associated with Commission Statements to determine what revenue might be exempt from local taxes.  I assume the 7-year rule should be applied.
On the other side of the coin, the information from the past 3 or 4 years does probably have value when looking at sales performance in support of the "where have we been and where are we going" planning.

There is mention of the "re-classifying" some information in the House Cleaning discussion.  The HouseKeeping options
          File | HouseKeeping | WholeSale Delete
includes options to purge Sales.Orders or Customers.
NOTE: "Purge" means to "physically remove", throw away, discard, and/or eliminate all evidence of its existence.  PLEASE create a backup before using these processes.

Sales Orders written on or before a specified date maybe discarded.  Pressing the F1-key while looking at the Purge Sales.Orders (50.31) window will bring up a page from the Help.Document concerning the process, how to use it, and what it does.
Customers with no activity after a specified date may be discarded.  This will include any and all related information such as Sales.Orders, Notes, etc.  Pressing the F1-key while looking at the Purge Customers (50.32) window will bring up a page from the Help.Document concerning the process, how to use it, and what it does.

So, how long do you keep it?  I don't know, that's your shot to call.  My guess is less than 4 years is too little.  How much longer than 4 years?  Ya got me, you'll have to think about it and make the decision based on the advice you receive, and the validity of past years activity.

Will it make any difference in performance?  Yes, but not enough to be a significant factor in the decision.  It WILL reduce the size of your backup file, which really isn't very important either.
That being said, the Utilities discussion talks about the result of holding too much stuff-there IS a limit to how much you can store.

Lessons from the School of Hard Knocks
These notes are the result of telephone conversations and email exchanges over the years.  The purpose here is twofold: