If germany concentrates power in Berlin and leaves just one infantry in coastal territories this is the best defence.
Because shore bombardment is useless and next turn germany recovers agin easily that coastal territory.
Sometimes it maybe more worthwhile to fortify both France and Germany. That way you are denying 6 IPC to the Allies, and those can make a big difference to the UK, and you’re not spending units retaking it.
Also, France has a VC. You may need to hold it for a round to achieve victory. Or, as in the case of the game I won as the Allies, you may need to hold it to stop Allied victory. I captured France with the UK, liberated Karelia with the US, and captured Kwangtung and Philippines with the US. Kwangtung was an oversight and the Japanese player didn’t think I’d attack Philippines. It wasn’t desperate on my part, but I didn’t think I’d get a better chance while USSR was still in the game because Germany was going the southern route.