Unless those online taxi services have changed, you only book a reservation when you are going to travel. We used Disney/Lyft one time and I was clicking around on their phone app to see how it worked and mistakenly created a request. Most of the time online purchases have a 'place your order' screen so it is clear you are ordering something. They did not and apparently there is a no-show fee if you try to cancel a reservation. I was able to call them and explained what had happened so they dropped the no-show fee.