At a given time, Wix can handle thousands of visitors or consumers on your site at the same time. However, this also depends on your plan. The amount of data and visitors your site can handle will widely depend on the premium plan of your site.
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While initially, you do not need to purchase any expensive plan just for the sake of bandwidth, with increased traffic on your site, you might need to buy a comparatively expensive plan to ensure that visitors do not face any issues.
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But this is not a problem because more traffic means good earnings and you can invest it on an expensive plan and more features to impress your visitors.