The 3205 has all the US
charts in memory. You would only have to buy chips if you want to go outside the US. The 3205 uses the proprietary Garmin chips that may be a problem getting in the future. This is just speculation on my part but it's been 3 years since Garmin has made a plotter that uses their proprietary chip. Then again, there may be some good deals on these chips on the used market. They've now gone to the generic SD memory cards which, generic, don't rely on Garmin for supply or reader/writers.
I own a 3206 and doubt that I'll get out beyond the internal
charts and the non US chips that I already have. One thing I did discover is the 3206 only has the US charts. The SoCal/Mexico chip necessary for the pre 32XX series covers the US south of Monterey but also includes
Mexico down to Acapulco. The 32XX series only includes the US charts as standard not
Mexico so you still have to buy the SoCal/Mexico chip with the 32XX and above if your going to
Baja or further south..