Good morning Li-e
Doing a restore could mean one of two things:
1. Restoring from a previous backup
2. Restoring to factory settings
If the first option is what you are talking about then it will just bring the iPad back to the state it was in when you did that particular backup. If it is the second choice then everything you have on the iPad will be completely done and it will be like you started it up right out of the box, meaning that it goes back to the initial factory startup, so not only do you lose the progress of your games but you lose all of your apps, settings, and information that was stored on it.
To answer your second question, it's a matter of preference. If you have the space to backup to the cloud then it wouldn't hurt anything, however the process could take longer. If you want a quicker backup and have access to it anytime you want then by all means backup to the computer. The thing with the cloud is you have to have an internet connection to access it. So if you are in a spot where you don't have internet access and you need to restore your iPad from the backup stored on the cloud, you wouldn't be able to. However if you had your backup stored on a laptop and you had that with you then all you would need to do is hook up your iPad to the laptop and reload the backup.
Again, it's a matter of preference. My preference is doing a backup to the computer. I hope this helps.