Just to add to my previous post:
1. If you know for fact that the agency you are programming in does not use a tone [which is common with a lot of paging frequencies for Fire/EMS], then set Squelch Mode to "None". Although "Search" will work, it'd be more efficient if it were just set to "None"
2. If you know the agency is transmitting a tone but you don't know if it's DCS/DPL or CTCSS/PL or a P25 signal with a NAC, set Squelch Mode to "Search" so that it will display it for you in the scanner and you can make appropriate changes.
3. If you know the agency is transmitting specifically CTCSS/PL ( or DCS/DPL or is a P25 signal with a NAC ), but you aren't sure what the exact tone / NAC value is, then set the Squelch Mode to CTCSS (or DCS or NAC) depending upon what you know and then checkmark "Search for Value"
I rarely use #3. Usually I either know the agency isn't transmitting a tone or I don't know if they are transmitting a tone and I want to know if it's CTCSS/DCS and it's value and thus set Squelch Mode to "Search"
The more you know, the more efficiently it scans though if you set it properly.
Mike