This approach can work for experienced speakers, in particular if you have spoken about the given topic before, but I'd strongly advise against not rehearsing for folks a bit newer into their speaking career. So often I have seen talks where folks either were time after half of their time slot, or they ran out of time towards the end. Or they lost track of the plot, went off on a tangent for way too long, etc.

All this is not great for the audience (who have "invested" into your session, by paying for the ticket, spending time away from work and family, not attending other concurrent sessions, etc.), and it can so easily be avoided by rehearsing.

The most common reason I have seen for folks skipping to rehearse is the awkward feeling you might have when speaking loud all by yourself. If that's the issue, it can help to do a dry run in front of colleagues. In any case, "winging it" is best reserved for later on, after having gathered quite a bit of speaking experience and having spoken about the same, or very similar, topics before.

I'd also recommend to avoid reading from slides during a talk as much as possible, it's also not a great experience for the audience. There shouldn't be much text on slides to begin with, as folks will either read that, or listen to what you say, but typically have a hard time doing both at once.

(All this is a general recommendation, not a comment on your talks which I have not seen)