What historical data is impacted by deleting inactive leads?

biggest issue is you will loose subscription info and if sales puts them back in the CRM and they sync down to Marketo you will not know that they have historically told you that they do not want Marketing emails...

Not so sure that example is true Mark. Durable unsubscribe.

Thanks for the responses. We are keeping all the unsub's and we don't have a CRM connected to Marketo. Time to reconsider how much we purge. 

I wish I hadn't marked this as solved, because I have thought about this some more, thinking through the impact to our analytics. Unless I'm wrong, and I hope I am, if I purge inactive leads it will impact even last week's data. 

Let's say I sent 100k emails last week with a 3% open rate. Today, I find 7000 inactive emails. If I purge them today, last week's open rate is now 3.2% (3000/93,000). All the 2013q3 metrics I put in last quarter's report to management, is going to be very different from the 2013q3 metrics I put in this quarter's report to management. No bueno. 

The reality - inactive leads have to be kept in our database if we want to protect the integrity of our data. Someone tell me I'm wrong.

You're not wrong. By removing inactive people from your database you artificially bump results up. It is a tactic people use to their advantage to show improvement over time. It can be a little decietful, but happens. :)

I thought about how people could use this to juice their numbers. I'm more concerned about consistently having accurate info to make decisions with and present to the people I report to. Never a dull moment with Marketo.

I also am about to delete a slew of old names and am expecting to lose all reporting. Is there any reporting that remains? Page visits? Flow through on model reports?