Assuming it was preceded by a colon, this:
:)))
means a much bigger smile than this:
:)
However, I’ve always thought it was a very poor way of expressing a big smile, since we already have this:
:D
to indicate a big smile. By contrast, the two extra brackets make it look like it’s a regular smile, but with multiple chins, as if the smiling person were seriously overweight.
As such, the smiley with multiple brackets is as big a fail as when people put in extra hard consonants when they are trying to indicate that they are stretching out the word for emphasis. So, if they mean to say:
Okaaaaaaay!
or
Okayyyyyyyy!
which tries to express in print what one might say out loud, but they instead write:
Okkkkkay!
this does not produce the desired result at all. How do you even pronounce that? Silly.