In essence ICEM Surf is a strict bezier patch modeller which will force you to create very clean surfaces. The downsides to this are that certain work flows can be a lot slower than with nurbs modellers, anything to do with circles needs to be split into 4 pieces and bezier patch modelling is very, very sensitive to where control points are placed. Very sensitive.
On the positive side you get beautiful surfaces which you can control and manipulate far easier than multispans. The match tool is an amazing beast of a command. I can’t model freeform without this now! So many things you can do while this command is active…
There are also the realtime sections and surface matching info which are priceless.
It crashes a fair bit too, so save often.
And you only have one undo, so focus your mind!
One warning - to get the best out if ICEM you really need to learn the techniques of bezier patch construction. There are many very specific techniques which in my opinion you will only learn from working in the Class-A dept of an automotive company. I was lucky enough to do this for a few years and learnt from some super talented bezier modellers. You just won’t get that knowledge from any where else I don’t think.
Another word of warning - you need to tweak your mind-set to understand that everything you create in ICEM is an approximation. So with every command you need to decide whether it’s within an acceptable tolerance or not. This adds time to the work flow.
A lot of stuff is just quicker in Rhino, for instance handrails and repetitive details. Also geometric patterns are quicker in Rhino. But good news is that you can exchange data easily between the two programs via IGES.
Do you need ICEM? - Only if your clients are demanding better quality highlights (reflections) across your surfaces or you have become obsessive about creating clean surfaces. But there’s a very high financial cost to pay for this…
@TomTom may have some further insights into this?