You don't have to polish if you are happy with how it looks. There is no reason to take off more clear than you need, even if it is a miniscule ammount.
After claying you have a few choices:
- Light polish, then wax
- Paint Cleaner/chemical polish, then wax
- Glaze, then wax
- Wax
The light polishing (fine polish and/or black pad) or the paint cleaner will make sure the old wax/sealant is gone before you lay down the new stuff.
Using the glaze is purely for cosmetic reasons and will boost the shine before you lay down the LSP. However, it won't get rid of the old stuff.
Waxing is the final option, but you would still have remnants of the old products still on the surface of the car.
I only polish once a year in the Spring. In the Winter I don't bother knowing the abuse the car will take will quickly undo any of my work. In the past I've used Klasse AIO (its more of a pain cleaner than anything else) to clean up the paint before laying down Klasse SG for my winter prep. Next year I'm going to branch out a little and am considering a product like Blackfire Gloss Enhancing Polish. It appears to be a glaze that also has some cleaning properties. If you read around here you'll find many other fine finishing polishes or paint cleaners in addition to the two I've mentioned that might fit the bill for you.