What I am trying to understand is there any benefit of implementing VLANs for this purpose?
it sounds like you're using CAPsMAN with local-forwarding off, so CAPsMAN is sending all your wireless traffic to a single router, and you control the traffic by having each SSID go to a different bridge on that router, right? in that case, you can use VLANs, but you probably don't need to.
where VLANs are useful is when you have multiple layer 2 networks (like the multiple bridges in your configuration), and you need to maintain that separation of traffic
between multiple devices.
for example: let's say you have one router and a bunch of APs, and you want to provide two SSIDs: a "users" SSID and a "guest" SSID (pretty typical setup). but your wireless users need to connect to servesr on the same L2 network, and you don't want all that traffic going to the central router and back, so you turn local forwarding on in CAPsMAN. that means instead of sending all the wireless traffic to the CAPsMAN router, the AP will add the wireless interface to its local bridge and switch the traffic itself. without VLANs, you could do this by having two bridges on each AP - one for "lan" and one for "guest" - but to connect both those bridges to the central router, you need two physical Ethernet ports on each side, one in each bridge.
now let's say your APs are something like hAP ac2, with a built-in switch, and you want to connect some surveillance device to one of the APs instead of running a cable all the way back to the central router. so you create a third bridge on the AP for the surveillance device, but now you also need a third cable from the AP to the router to carry that traffic. clearly this isn't a workable setup (unless you really enjoy running new cabling).
instead, do it like this: create
one bridge on each AP, and create three VLANs: VLAN 101 for "users" SSID, VLAN 102 for "guest" SSID, and VLAN 103 for surveillance devices. then configure CAPsMAN to tag the wireless traffic appropriately for each SSID (101 or 102), and configure the bridge port with the surveillance device with PVID=103. now your single bridge has three virtual networks, which behave more or less the same as the configuration with three bridges did: the "users" traffic is in VLAN 101, the "guest" traffic is in VLAN 102, and the surveillance traffic is in VLAN 103. but now you can run a single Ethernet cable from the AP to the central router, configure it as a tagged port in each of the three VLANs, and the traffic from all three VLANs can go back to the router over the same cable. (this works because the AP will prepend a header to each Ethernet frame containing the VLAN tag, so the central router knows which VLAN the traffic is on, and the router will do the same when sending traffic to the AP.)
on the central router, configure the same single bridge with three VLANs, and then create three VLAN interfaces (/interface/vlan) called "vlan101", "vlan102" and "vlan103". these work like normal Ethernet or bridge interfaces, but they only see the traffic in the particular VLAN they're configured in. now you can assign 192.168.1.1/24 to vlan101, 192.168.2.1/24 to vlan102, and 192.168.3.1/24 to vlan103, and process the traffic normally in the router as if each VLAN was its own physical network.
tl;dr: VLANs are like having multiple bridges, except the traffic for all the bridges can be carried between devices over a single Ethernet port.