Whats ther pourpous of live rock

i have like regular rock kinda is that bad but i have a fish only tank

 

I'm not sure of your question but I will give it a shot.
Any live rock is good as it will help filter your system as it does in nature. You can turn regular rock into live rock by allowing it to seed in your system where you already have some live rock or live sand, and the bacteria / critters will grow in population and do the same. If your question is in regards to porous live rock that just means that there is more surface area so that more filtering would be able to take place.
If this did not answer your question just let me know.