From Socs Info Wiki
This document provides information related to process niceness.
If you expect your process to be a CPU hog, before running it, you can specify a "nice" value with the command "nice".
If your process is already running, and is a CPU hog (ie. it uses a considerable amount of CPU time), you should "renice" your process with the command "renice".
The default "nice" value is 0 (zero). A user may only increase the nice value - never decrease it. The maximum nice value is 19 (or 20, on some systems). The greater the nice value, the nicer you are to other users of the system (because your process has lower priority).
The concept can be compared to waiting in a queue at a store. If you have a big load of groceries, and someone behind you only has two or three items, you might decide to be nice and let them go ahead of you.
If you don't nice (or renice) heavy processes, and the system staff notice, your processes will most likely be reniced to 19 - the most nice, and least priority (ie. your process will run only when the CPU has nothing else to do).
Therefore, it is better to be proactive by setting the nice value yourself, to say, 10. But that is just a suggestion... you are free to experiment. Take note of the priority number as you change the nice value. Use the command "top" to monitor your process and watch its NICE and PRIORITY values change, as you use "nice" or "renice".
If you notice that one of your processes is running excessively long without dying, you should terminate it yourself, by sending it an appropriate signal with the "kill" command.