I know that seperate a LAN with VLANs it increase security but also the bandwidth of the lan links.
What is the max number of PCs that should be located to a LAN and despite the security but have only in mind the increase of the bandwidth of a LAN when we should seperate a LAN to VLANs.
For examble a LAN with 20 users is it wise to seperate to 2 VLANs.
As a rule of thumb, it is advisable to maximize the number of hosts per vlan to about 100-150. The actual setup will largely depend on the applications that are used. If these are very bandwidth-hungry, you will need to reduce the amount of hosts per vlan.
Another issue is the amount of broadcast traffic on the network. (less = better)