From personal experience I can't tell whether is has any effect. For winter storage I flake but during the 5 months of sailing I just thrown it in the bag. My spi is from 2003 and the first two causes for spi degrading are respectively; being blown-out (1 to 2 years), damage from the retrieval line.

I'm still using this spi despite its sticking spi tape retrieval line damage repairs. But you can feel it is really blown-out and have been for some time.

I have yet to see any damage from not-flaking and wouldn't even know what kind of damage that can cause.

Wouter