It depends on the location and type of purchase, but it is always a bit of a risk.
Most on-demand parking locations allow you to go in and out of the lot without issue - however it is at your own risk. Once you leave your spot, you can return and park in any available space, but your space is never guaranteed. You must also always obey the rules of the parking lot - if there are no In and out privileges available it is often posted onsite or listed in the zones description in the app.
Reservation locations are different. Most of those do not allow in and out privileges unless otherwise noted as they usually require you to scan in and out one (1) time to utilize your reservation.