Good to use different machines and exercises -- quickly discover there's all those little muscles you haven't been using.
Also good to start conservatively on new machines. Like you haven't been doing anything for 6 months. So you don't hurt one of those little muscles, or some little muscle fiber somewhere in one of the bigger muscles... oops.
The old free weights .vs. machines argument. I pretty much agree with the free weights folks. But despite agreeing in principle, I've been using the machines since I started using the campus fitness center just because of convenience.