Changing your root zone depth (RZD) won't necessarily use more water (overall), it will adjust your bucket size (how much water it takes to fill up your zone, and how long it takes to get fully depleted over a number of days) which will change how frequent (or infrequent) you are watering (which can be tracked on each zone by viewing their soil moisture graph).
I would probably start with one or two zones in a flex daily schedule to see how well they track (using the default RZD) for a bit, and if you need more frequent/infrequent watering you can adjust RZD or crop coefficient (easiest way to adjust frequency).
For our next major software release we are working on an easier way to allow folks to adjust flex daily frequency with a simple adjustment and not necessarily have to understand all of the advanced settings (if they choose not to).
Here are some quick ways to adjust flex daily
This has a good synopsis of all documentation pertaining to flex daily
Hope this helps!