Should i erase the previous windows after upgrade ti win 10?

I already have windows 10,but my question is:should I erase the previous version of windows? I had windows 8.1 home before ,should I erase it or keep it just in case of have to restore it for any problem with windows 10? please help,thank you.
 
I would definitely keep the old Windows for several months more. At this stage, you cannot judge how Win 10 will develop, and you might find it starts to change in ways you do not like.

Such as becoming more intrusive, extracting too much of your private information, requiring indefinite future payment for features which turn out not to be optional, and you may at any time learn that MS has been hacked, and half-the-worlds details have gone missing......ok it would be too late then anyway, but you get my drift ?
 
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