Why break DHCP into classes?

Question

Cisco

Often in the configs for Cisco routers I see the following entries:

ip dhcp pool dhcppool
   network a.b.251.0 255.255.255.0
   domain-name namelevel2.namelevel1.com
   netbios-node-type h-node
   default-router a.b.251.254
   option 128 ascii "Nortel-i2004-A,c.d.0.56:4100,1,5;c.d.0.56:4100,1,5."
   dns-server a.b.0.1 c.d.0.44 c.d.0.43
   netbios-name-server a.b.0.1 c.d.0.44 c.d.0.43
   class cd-workstation
      address range a.b.251.10 a.b.251.250
ip dhcp class cd-workstation

I am tormented by the question: why do I need to specify class cd-workstation and then apply it below for the same pool ( ip dhcp class cd-workstation command )
There is also a related question: how can I assign one address pool to several vlans. Maybe that's what classes are for?

Answer 1

DHCP classes allow you to "filter" DHCP requests by options and bind them to different pools.
More details, for example, here - www.cisco.com/en/US/docs/ios/12_4t/ip_addr/configu...
PS Classes are not needed to stretch one pool into 2 vlans, but why do you need one pool for 2 VLAN to stretch?

Answer 2

Situation:
Core - Cisco 3750
Access - Cisco 2960
There are 40 computers in the accounting department, 12 of them have Internet. Now they all work in the same vlan and receive IP addresses from the DHCP server running on the Cisco 3750. There is only one address pool.
Separate people who have Internet and who do not have it into two vlans, while maintaining addressing. I would not want to fence a lot of pools, since there are a lot of such departments.
There may be a better solution that I'm not aware of. Tell.