Benefits - 3Com corebuilder 3500 Implementation Manual

VLANs provide a high-performance and easy-to-implement alternative to
routers for broadcast containment. Using switches with VLANs:
Each network segment can contain as few as one user (approaching
private port LAN switching), while broadcast domains can be as large
as 1,000 users or even more.
VLANs can help network administrators track workstation movements
to new locations without manual reconfiguration of IP addresses.
VLANs can be used to isolate unicast traffic to a single broadcast
domain, thereby providing a form of network security.

Benefits

You can use VLANs to:
Reduce the cost of equipment moves, upgrades, and other changes
and simplify network administration.
Create virtual workgroups in which members of the same department
or section appear to share the same LAN, with most of the network
traffic staying in the same VLAN broadcast domain.
Help avoid flooding and minimize broadcast and multicast traffic.
Reduce the need for routing to achieve higher network performance,
ease of administration, and reduced costs.
Control communication among broadcast domains.
VLAN Overview 157