Sometimes yes. Even if the final image is only displayed on the web, a digital medium-format system can still offer advantages during capture.

From the community answers, the main benefits are:

• larger sensor characteristics, which can improve fine detail rendering and overall sharpness when used well
• the ability to achieve different depth-of-field and background rendering (“bokeh”)
• stronger image quality for subjects where tiny details matter

For luxury products like watches and jewelry, that extra detail can matter a lot. The images may also serve as archival records or premium marketing assets, not just small web graphics. In that context, “a little bit sharper” can be valuable.

That said, medium format is not automatically necessary just because the files end up online. Lens quality, lighting, technique, and workflow often matter at least as much. If your Rebel looks close, that may reflect the fact that web output hides much of the difference. But for top-end product work, especially with very expensive lenses and careful studio use, medium format can still be justified when the goal is simply to get the best possible image quality.