As hiegtx said WHAT, and HOW, you want to scan and monitor is your preference.
For smaller counties I think you can have ONE Favorite List and you should be OK.
For a Larger County like Lucas you'll need to determine how you want to monitor.
Scanning a larger county with one favorite list you may not be able to follow particular separate calls ( ie: Police, Fire, EMS, Sheriff, State Patrol. ) You might hear a transmission on a County Channel, then the next you'll hear a transmission on a City Channel missing the response on the County Channel. So you end up hearing bits and pieces from several departments but miss the whole picture.
The reason I have set mine up the way I have is that first of all I have 3 scanners going at one time.
On my SDS200 I monitor Napoleon City, which includes Police, Fire and EMS and temporarily lock out the rest. BUT I have the capability to monitor SOME, or ALL of the rest on that scanner, if a situation arises that I need to.
On my BCD325P2 I monitor Henry County, which includes Sheriff, County Fire, and County EMS and temporarily lock out the rest. BUT I have the capability to monitor SOME, or ALL of the rest on that scanner, if a situation arises that I need to.
On my Home Patrol 2 I monitor Defiance County which includes Sheriff, County Fire, and County EMS. I also monitor Ohio State Patrol District One, and temporarily lock out the rest. BUT I have the capability to monitor SOME, or ALL of the rest on that scanner, if a situation arises that I need to.
Why do I do it this way? There are times that there is radio traffic transmitting from Napoleon Police, Henry County Sheriff, and Defiance Post of the Ohio State Patrol - AT THE SAME TIME ( ie: a pursuit ) - and if I had all in the same Favorite List, or on the same scanner, I would miss some radio traffic. This way I can scan WHAT I want, but not have the increased scanning time on a scanner by re-scanning the same system multiple times like hiegtx said. Also, I temporarily block ALL the other departments I have in other favorite lists, but can un-block them if I need to, so I can pick up their transmissions if need be.
Now, I've been scanning since the 1970's, when we installed crystals into scanners, and I know what I want to scan and how I want to monitor radio frequencies.
Since you're starting out, I would recommend that you go to Lucas County in Radio Reference and decide WHO you want to monitor - and HOW you want to monitor them - with only ONE scanner. Once you accomplish that you need to decide your priorities.
If it is a particular area of Lucas County, and you want to monitor SO, FD, and EMS from that area, then put that in a Favorite List.
If you want to monitor ONLY Lucas County law enforcement in an area, then put that in a favorite list.
If you want to monitor ONLY Lucas County fire in an area, then put that in a favorite list.
If you want to monitor ONLY Lucas County EMS in an area, then put that in a favorite list.
The point being - only YOU can decide WHAT you want to monitor, HOW you want to monitor, and HOW MANY favorite lists you want to create to do so, with the least amount of re-scanning the same system multiple times.