Sometimes you need a table - if the system is a true P25 system with a 9600 baud CC, you don't need it, as the required information is contained in the control channel.
You also don't need it if ALL the frequencies in the system have a 0 in the fourth decimal - if any of them have a 5, and the system is an analog or mixed type (both analog and digital on the same system), then you will need to have a custom table
All of this applies to Motorola systems
Slight correction:
For the Motorola Type II systems (not the true P25 9600 baud CC systems, as Mike has noted), the key is the fourth decimal place. However, the custom band plan is needed if any of the frequencies in the 851.0000 to <854.0000 have a
zero in that #4 slot (i.e. 853.3750). If
All of the frequencies in that range (851.0000 to <854.0000) have a
five, then the custom plan is not needed.
Two systems from the DFW area for an example:
This rebanded
system has eleven frequencies that are above 851.0000 abd below 854.0000. However, no custom band plan is required, as all of those frequencies have a
five in the fourth decimal place.
On the other hand,
this system requires the rebanding tables. It has one frequency, 853.4250, in the 851.0000 to <854.0000, that has a zero in the fourth decimal place. Unless the custom tables are used, the scanner will not fully track the system, tuning to an incorrect frequency when the 853.4250 voice channel is utilized.
And, no, it does not matter if the tables are present when not needed. The scanner will still track the system correctly.
The main difference that the presence of either a 5 or a zero in that fourth slot makes is whether an older scanner, that is not rebandable, is still usable on the system.