If I have NAT or PAT applied on edge router, Would it matter if I use IP addresses from public block in my LAN? And how?
I'm assuming you're considering using an IP block that is not registered to you. Otherwise, skip to the last paragraph.
Besides being a very poor practice, if you use public addresses on your internal network, that means that you can never reach hosts that use those real addresses. You may think you'll never need to reach servers in some other part of the world, but you'd be surprised at how often that happens.
BTW, if you don't use NAT, you're essentially hijacking someone else's addresses, and your ISP may disconnect you from the Internet (among other things).
The RFC 1918 addresses (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) should provide plenty of address space for your internal network.
If you are using your own IP block, then there's nothing wrong with using those addresses internally. It may possibly increase your security risks, but those can be mitigated by other means.
It matters in the situation that you do not need/want to reach those public IPs used.
If you use such IPs and then you, for example, want to access a site that has one of the IPs, it will not work, because your IP will resolve locally instead of going through your edge router and forward.
My company also uses such a system (it was implemented this way to be able to connect to other partner locations via EIGRP) and the corresponding IPs are assigned to China, so things should be fine as the company does not deal anything directly with something in hosted in China.