Miwaa
Saver bookings cost less than Regular ones (obviously you can see that already in the screenshot you shared).
The main difference is the waiting time. Basically, saver bookings are given lower priority compared to regular bookings.
1. The booking will take longer (since delivery drivers or riders may choose to not accept and/or even avoid saver bookings since their take home pay will be less than a regular booking)
2. The delivery will take longer (but should still be within the prescribed delivery window period) as it is not a priority ASAP delivery
These inconveniences are what you get in exchange for paying less.