If you have 4-5 computers.Then un0managed will be a good option.If you have laptops that rarely come log into the network or most work from home still unmanaged will be a good option.
But if you have more than 5-10 computers in the network.Then having a SEPM manager would be a good option.
Managed vs Unmanaged
Only the SEPM will download the defintions and all the clients will retreive it from SEPM.In unmanaged all clients will download the definitions.
In Managed environment
You can monitor all the clients activity and logs at one view.You can set or change policies whenever you want
However in unmanaged you will have to go to computer to computer to do that.
So if you have more than 5-10 computer all in the network Having a manager will be the right option.