This insight can help you understand your contacts and the corresponding stages of lifecycle that they are at in the form of a funnel insight, within a given time period.
From HubSpot: Lifecycle Stages help you organize your contacts based on the stage they are at in your sales cycle: subscriber, lead, marketing qualified lead, sales qualified lead, opportunity, customer, or evangelist. Since your interactions with your contacts vary depending on what lifecycle stage they are in, it is helpful to have the ability to segment your contacts. For example, HubSpot's marketing team uses lifecycle stage settings to ensure that our customers do not receive emails intended for prospects and leads. Depending on the structure and needs of your business, you may find yourself using all of the Lifecycle Stages, only a few of them, or creating a custom contact property that functions in a similar manner.