If I remember correctly, even if you use the same vrrp group number, if you are configuring interfaces that are in different networks (i.e. VLANs or broadcast domains) the vrrp instances are still distinct in that they operate independantly and will send a VRRP message for every interface.
If you want to limit the amount of VRRP protocol traffic, you may want to look into the 'vrrp-inheret-from' config statement. That ties all of the vrrp groups together. Keep in mind if you do that you can't do any load balancing, i.e. you can't have some subset of VLAN gateways active on one switch, and the others active on another switch. With the inherit-from you could I think break out two broad groups so you'd have two (effective) vrrp groups, one composed of hald the VLANs active on one switch, and the other group of VLANs active on another switch.