If you create 10,000 strings in a loop, a lot of garbage collection has to take place which uses up a lot of resources.
If you do the same thing with symbols, you create
If you refer to the same symbol in your loop, then it doesn't have to recreate that object everytime i.e.
while i < 10000
i += 1
:im_using_this_symbol_here
end
Now if you use a string there instead, the string will be recreated 10K times. In general, use symbols in cases where you almost treat the literal like a constant or a key. A very good example for me would be
link_to "News", :action => 'news'
instead of
link_to "News", "action" => 'news'
action being re-used over and over again within your application.