I think you need to do an import first, so it is faster to just rollback to a snapshot than re-import each time. I prefer snapshots so I can configure the network as needed for our corporate environment (saving me from doing that each and every time).

If you save the zip file you need to do the following:

1. extract the VM bundle

2. install and configure the VM (this is automated but can take up to several minutes)

3. boot up the VM

By using a snapshot you skip steps 1 and 2 and resetting a snapshot is pretty much instant, so you're only left with step 3.