The selector has been inserted in all the reports in which the date and time of the calls are reported, or in which talking about dates is in some way significant: it has not been included in the Phone Bill report, for instance, as it is not significant for that particular case.
Once you select a TZ, all the dates and all related fields in the report will be expressed using that time zone.
That means that moving from one time zone to another, you can immediately appreciate the time change that will bring the entire report to the time zone you have selected! Plus, if you decide to schedule the report, it will also be expressed in the time zone of your choice.
Same thing for filters: if you filter the report on a specific date, it will continue to be consistent with the TZ expressed in the selector.
Below you can see the effect of the time zone change on Grouped Time Dimension Chart. Isn’t it amazing?