I would say test and see. Ideally A/B test, if that is too much hassle just try having them on and off for alternate days and see if you get more shares.
Of course whether shares help sales is another question....
A lot of the time if people want to share they will do so regardless of whether you have buttons or not. Likes for an FB page might be different.
Also, you can create share and like links without loading the social media networks own tracking code laden javascript to slow down your site.