digital logic - In IC design, what is the Buffer for ?

In CMOS design, we always use two inverters as a buffer, but at some point, I dont quite understand the functions or importances of the buffer.

As I was told before, 1) the buffer could smooth the output, but why ? It is two inverters, for example, if I design a ring voltage oscillator consisting of many inversters, why do i still need two inverters to the output of the VCO ? How can this buffer to smooth the ouput of VCO. 2) Also, the buffer usually can drive the big load (cap or res ), this is totally blurry for me, I dont understand it.

I just know these two buffer's function, and I even dont understand it why it has such functions, and for other use, I am not sure...

Hope get more help to understand this small but important block...