Reusing presentations is often a necessity due to time constraints. But, having the same slides / handouts, doesn't mean that you need to say the same thing. Generic presentations waste time on ideas that don't need explaining and glossing over concepts that may be confusing to your audience. If possible, do some research on who you're presenting to, so you can make a best guess at how to make the most efficient use of your time together.
A good way to do this is to share your materials ahead of time. But, if you're going to use this approach, then it's even more important for you to make a conscious effort not to read off of your slides / handouts. Otherwise, your presentation is completely redundant. Focus your presentation on clearing up confusion, preferably skipping the parts that your audience already understands.