When does extra RAM helps?

Well, little question for your guys When does extra RAM helps?
To my knowledge, linux always make use of all the RAM avalaible as disk cache

So, when exactly does the machine starts swapping?

Code: 
             total       used       free     shared    buffers     cached
Mem:           494        463         30          0         33        294
-/+ buffers/cache:        135        359
Swap:          996        246        749
Would adding 512Mb helps?

 

 

 

 

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