CISCO WLC: use LAG or not

Yes, the 2504 supports LAG in v7.4. Your first guide refers to v7.0.116.0 and the second guide written in 5/2013 implies v7.4. Enabling LAG requires a reboot of the WLC and has limitations similar to the 5500.

When LAG is enabled on a WLC, the WLC forwards data frames on the same port on which they were received. The WLC relies on the neighbor switch to load-balance traffic across the EtherChannel. The WLC does not perform any EtherChannel load-balancing on its own.

Limitations/Restrictions, same as 5500 but note 5508 doesn't have ap-manager inf's:

• LAG requires the EtherChannel to be configured for 'mode on' on both the controller and the Catalyst switch.
• The load-balancing method configured on the Catalyst switch must be a load-balancing method that terminates all IP datagram fragments on a single controller port. Not following this recommendation may result in problems with access point association.
• The recommended load-balancing method for Catalyst switches is src-dst-ip (enter the port-channel load-balance src-dst-ip command).
• With LAG, all of the controller ports need to connect to the same neighbor switch. If the neighbor switch goes down, the controller loses connectivity. With multiple AP-manager interfaces, you can connect your ports to different neighbor devices. If one of the neighbor switches goes down, the controller still has connectivity. However, using multiple AP-manager interfaces presents certain challenges when port redundancy is a concern.
• Port mirroring is not supported when link aggregation (LAG) is enabled on the controller.

Assuming a Cisco WLC... Go to "WLAN > Select the WLAN Profile > General Tab > Radio Policy"

Updating my answer to clarify a few things...

• 802.11a operates at a maximum of 54Mbps, only in the 5GHz bands
• 802.11b operates at a maximum of 11Mbps, only in the 2.4GHz bands
• 802.11g operates at a maximum of 54Mbps, only in the 2.4GHz bands

Keep in mind that wireless operates in unlicensed frequency spectrum, so it is a bit like the wild west... Many corporate networks choose to marginalize support for 802.11b/g where possible, due to the rampant use of the 2.4GHz frequency spectrum by consumer devices... today, 5GHz (and thus, 802.11a) tends to have much lower background noise levels, so it is more suitable for business voice and data services... however it also doesn't propagate as well due to the smaller wavelength in 5GHz signals. Use care when you disable 802.11b/g... it might be worth checking for coverage holes, if most of the traffic formerly used 2.4G...