Won't slow your computer down while you run bots
Allows you to run more bots at one time
Your computer doesn't have to be on whilst bots are running on your vps, saving hassle and money on your electricity bill.
You might be able to find a free trial SOMEWHERE but I doubt it. Either way- you get what you pay for (which in this case would be close to nothing). I personally recommend RSBotVPS, as do many others, but the prices are higher than some providers. For anyone who asks a 'beginner' question about vps's- i'd definitely say go with rsbotvps because #1 setting it up is not easy for everyone even with guides #2 you WILL eventually have problems and will need help solving them.
Keep in mind that pretty much any provider selling VPS's for less than rsbotvps has probably banned botting or will once they notice people doing it. Make sure you check back with whatever site you pick to make sure!
Other advantages:
-can access from any computer with internet
-separate from your IP so it would be potentially harder for jagex to catch you if you don't bot on a main (but you prob don't need to worry about this anyway)