Hi!
In Resume:
Visibility - It's just turning on/off the visibility of the component. The part will be counted in BOM, constraints stay active, etc. It saves some memory in the graphics card. You can do some visibility schemes and you can use them as filters to do specific part lists in drawings...
Suppress - It's kind of deleting the part (but temporally). The constraints or other aspects are also suppressed. It will not be counted in BOM. Also, you can create different Model states to create several scenarios of the assembly and use them as a filter in drawings. Suppressing components will save computing memory, so, in big assemblies, it can be used to gain computing performance by suppressing some components that you're not working on at the moment.
Activate - it's just a status, where you have the part in the workplace, but you can not select it. There are some uses for that, for example for use in reference parts, when you need to see the part, but you don't want/need to be able to select it.
CCarreiras