Each of the ASAs have a specific number of "VLANs". That is really what it is talking about here--802.1q sub interfaces. These range from 3 to over 1000. Note that the 3 is on the 5505 which is actually constructed a little differently.
I've never heard of a specific limitation on an interface that would restrict it beyond the larger number. In other words, I think that in almost all cases you could create the platform maximum number of vlans on one interface and not use any subinterface on any other physical interface. I've not personally tried that though.
I was thinking that alright, you can assign whatever number of Vlan the device can handle, to a sub interface. I just thought it might be some type of policy running in the background dividing up the bandwidth for each sub-interface created on the physical interface. Or maybe this is something the engineer has to do
@Richy165: Good point on the backplane limitations of the device.
Thanks for the input guys
Theortically you can create hundreds of sub interface on your ASA firewall but practially you won't do this becasue the bandwidth of the physical interface is divided among the all sub interfaces and which will create traffic problem on your network. There is a preconfigured policy on Cisco ASA which takes care of bandwidth allocation to its sub interfaces.
Network Security Specialist