why pointed portion is not left anywhere in an electrostatics a machine ?

At the pointed portion the electric field  intensity is very  high , because  $\mathit{E}\mathbf{ }\mathit{\alpha }\mathbf{ }\frac{\mathbf{1}}{{\mathbf{r}}^{\mathbf{2}}}$
at pointed portion  can be  consider as sphere  of very small  radius (r) , and the value  of  E  will be very high  and it  might  make the  near  by air  conducting  which  may  result  in  electric  shock .