CombineMesh Location and using multiple instance of same prefab ?

Hello !

I'm trying to optimize my game and ran into the CombineMesh script. It's said to be found in the standard assets but I saw that since unity 3, standard asset has been split into many packages and I can't seem to find the script in any of them... I googled it but it seems like I'm the only one to be dumb so, can anybody tell me where is it ?

I'm also wondering if it's the best way to optimize graphics for statics object or if something else came up ? Is the static flag enough or combineMesh (or something else) really make a change ? I'm actually using many many instance of the same gameobject : I have a long fence in my game, and also a lot of buildings. The fence (same for buildings) is in the asset store and I replicated it many times (maybe 50 instances) in order to have my complete fence around my garden. I'm quite new to unity so I don't know if it's the best way to do that or not ? Is there some sort of mecanism to build the world of my game (the statics element) in an efficient way ? Where can I find good practice for that ?

Thanks in advance for your help !