Uniden x36 scanners - without application a GPS or other special programming - will try to scan all of the sites and frequencies that you have programmed and enabled - looking for any active and decodable control channel. This will certainly slow down the switching from one site to another - even if stationary. On large systems, you can watch and see the scanner display one after another all of the sites being checked (even those not in range). Also by default, Uniden Sentinel programming software loads ALL site frequencies for the sites that you program for a given system.
This is not accurate, at least if you program your Favorite List competently and have Location Control turned on in the Favorite List settings. When scanning from the main database or a favorite list with Location Control enabled, the scanner will only scan what it thinks are nearby sites, based on either GPS data (if one is connected), or a manually entered location. Location Control is always active when scanning the main database, or the scanner would try to scan every licensed frequency and system in the USA and Canada.
You don't need a GPS - it's an option (and my description - "a toy") and it is still far from perfect for various reasons - but you don't need it. If anything, the GPS is needed only because Uniden didn't implement any smart logic to determine which site to scan. Like all of the programming, the GPS relies heavily on the data submitted by RR users which contains many errors that potentially affect what you hear (or don't). The GPS also has what I feel is a nasty side-effect in implementation in that it also controls which talkgroups get monitored at any given time. You can overcome it but not without alot of manual programming.
This is also mostly inaccurate. If the scanner is only used as a base station, you do not need GPS. You can enter your location once, and the scanner will remember that location until you change it. But if you use the scanner in a vehicle, it is not a "toy", it is a critically important feature. Not having it makes programming much more complex--you must assign quick keys to everything, and remember those quick keys, and enter them into the scanner WHILE DRIVING to toggle things on and off as you travel. This is not only an enormous hassle, but a major safety issue comparable to texting while driving.
It is true that there are erroneous entries in the RR and Uniden databases, but most of the data is correct, and updates are available weekly. The data in the database has gotten better over the years, and there is no reason to believe it won't continue to do so. And submitting a correction to the RR database isn't that hard.
And Location Control of Departments (groups of talkgroups) is a feature, not a bug. I don't see the point of trying to monitor a talkgroup from a PD on the other side of the state that isn't carried on the local sites anyway. Statewide talkgroups are put in Departments with statewide service range (or should be).
Scanning with a GPS while traveling isn't perfect, but it beats all of the alternative approaches hands-down, and is getting better over time as errors in the RR/Uniden database are corrected.