If you're specifically asking because of memory use, there is no need. Memory management in Linux is extremely efficient, and since everything is a process, a properly killed process doesn't block reclaim of that memory as you see a lot in Windows. You may see your "free" memory as being low, but that's kind of a misnomer as you should be paying attention to claimed vs unclaimed/cached memory, which will be "recycled" into other processes that request it. If you run into memory issues on Linux or BSD, you'll know it.

That being said, if your machine isn't suspending or cleeping, then you're just wearing your components out by leaving them on 24/7, so shutting down or suspending would be good practice to extend the general lifespan of your machine.