We have the same challenge.
Our sales team thinks its useful to have the previous engagement history for future conversations with either that lead at his or her new firm, or with other contacts at his old firm. And they'll point to that one time it was useful to justify keeping thousands of old records.
We're starting to make some headway by chipping away one or two categories at a time.
One thing we've agreed on is cleaning up data to remove contacts at organizations that no longer fit our Ideal Client Profile. The company refocused several years back, and many contacts entered prior to that point work for firms that we won't ever sell to. For example, we no longer sell to banks, so we can remove all banking contacts. While not a complete clean up of invalid contacts, it does get a substantial number out of the system.
The next area was getting them comfortable removing invalid contacts that never engaged--either directly with a sales rep or with a marketing campaign. This was more difficult because the company fit our profile. However, the lead never clicked on an email or filled out a form over the time they worked at their old firm, there's no real history worth preserving.
We're also looking at job titles or functions that don't make sense. some of our now-departed reps would enter every contact they could find at a target organization. Depending on your business, you may find that there is no reason to have Warehouse Managers or Controllers in your data. I'm getting some agreement on removing those names.
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