Well, it really depends on how the digitization of Helvetica that any particular user has installed is hinted. The Helvetica that comes with MacOS is quite nicely hinted, and will make for a pleasant read at most sizes.
On Windows, however, Helvetica isn't (at least from my experience) as nicely hinted, or at least doesn't play quite as well with Microsoft ClearType. And that's if it's installed, which is less likely on Windows. In that case, if your font stack specifies a fallback to Arial, which is ClearType's best friend, you'll probably be fine.
On Windows, however, Helvetica isn't (at least from my experience) as nicely hinted, or at least doesn't play quite as well with Microsoft ClearType. And that's if it's installed, which is less likely on Windows. In that case, if your font stack specifies a fallback to Arial, which is ClearType's best friend, you'll probably be fine.