After coming across the code golf trivia around the site it is obvious people try to find ways to write code and algorithms as short as the possibly can in terms of characters, lines and total size, even if that means writing something like:

    n=input()
    while n>1:n=(n/2,n*3+1)[n%2];print n

So as a beginner I start to wonder whether size actually matters :D. It is obviously a very subjective question highly dependent on the actual code being used, but what is the rule of thumb in the real world.

In the case that size wont matter, how come then we don't focus more on performance rather than size?