What's the difference between bulk delete and individually removing members/groups?

The data cleanup of inactive members, the individual member remove and the group expunge features all work slightly differently.  Here's a summary of the differences.

Who can be removed

The data cleanup is restricted to inactive members.  Individual member remove and group expunge can be used for any members, with some small restrictions (e.g. the member has pending orders)

What gets deleted

The data cleanup will delete all orders and financial activities for the members who have been deleted.  These are not deleted when an individual member is removed, or a group is expunged.

Note:  in all cases, the member's personal details, subscriptions and event tickets are removed.

Why make them different?

The data cleanup feature is there for organisations to easily and conveniently remove members who are genuinely no longer active in the organisation.  It is also useful for those who want to keep their WebCollect annual fee down - the annual fee is based on the number of members associated with the organisation.  

It is much easier to accidentally delete people you shouldn't when looking at a long list.  Deleting is a one-way action, and cannot be reversed.  We don't want errors showing up due to members' orders being deleted, which still have automated updates coming through from GoCardless, Paypal or SagePay, and we don't want to hear that you have accidentally wiped a bunch of active members by mistake.  So the data cleanup is restricted to those who are genuinely inactive.

That doesn't mean that you can't remove them.  The individual remove feature, and group expunge allow you to remove active members.  These don't remove the orders/financial activities, so you retain a financial record of your dealings with the members.  You do have to visit their member pages to do this, and therefore have an opportunity to check/review that you definitely want to remove them.