We use Schedule Reminders to set up email series for a very wide range of interest groups. With conditional funnels using smart groups, like Mailchimp conditional campaigns.
The easiest way to initiate these Schedule Reminders is from activity types, but we've hesitated to make an activity type for every new event or campaign since we'd soon have many hundreds. Instead we make activity types that cover generic topics and then use groups to limit which people will receive schedule reminders. It's a bit of a dangerous method - if you forget to limit a schedule reminder to a group you could send out emails to many people who haven't asked for them!
So... would there actually be any impact in terms of performance if we were to have many hundreds - perhaps eventually a thousand or more - activity types?
Thanks for your thoughts!