Why not always use -server option?

Question

Hello!
I've tried running some my applications with -server option - and discovered that for non-GUI apps -server renders drastic increase in execution speed.
For example code below takes only 2 seconds to execute with java -server while it takes more then 120 seconds with java -client option.
Now I'm considering writing all apps with
Runtime.exec("java -server MyApplication");Can someone tell me in what cases -server is a bad choice, and when it's OK?
And, in my code - does java runtime really create 1000 threads - or is there some optimization?
        public void run()
                int q=0;
                for (int i=0; i<10000000; i++)
                        q++;
        public static void main (String args[])
            long l_start = System.currentTimeMillis();
                for (int h=0; h<1000; h++)
                        new Hell().start();
                System.out.println("Operation took "+(System.currentTimeMillis()- l_start)/1000+" seconds");

Answer 1

JVM tutorial states that there are the cases when server performs slower. If you going to execute a small utility (<20 sec), use client.