Those metal tabs on the sides of your dimmer are heatsink tabs. They can be removed or they can stay attached, but keep in mind that the maximum loads listed in the switch's manual apply only if all tabs are attached. This stipulation only applies to our ZEN22 Dimmer, ZEN24 Dimmer, and ZEN27 Dimmer, not our on/off switches.
It's completely fine to remove the tabs if you need extra space in your gang box, and many users opt to remove them for double-gang and triple-gang set ups. But here are the rough load capacities that you can expect with all 6 tabs, 3 tabs, or no tabs.
For ZEN22 and ZEN24:
When using LED or CFL bulbs, the maximum load with all tabs attached is 150W for the ZEN22/ZEN24 dimmers and 100W for the ZEN27 dimmer. But just with incandescent (resistive) bulbs, maximum capacity will decrease with each heatsink tab removed. It's difficult to specify an exact load capacity with LEDs since they're inductive loads whose power draw spikes and drops frequently. However, we wouldn't recommend having more then 60W of LEDs on load for a ZEN27 dimmer with no tabs. We wouldn't recommend having more than 90W of LEDs on load for a ZEN22 or ZEN24 dimmer with no tabs.
If you have any questions about your dimmer or want to verify if the load you plan on connecting will work with a given number of tabs, let us know. We'll be happy to help with that.