It depends on your task. That's it.

I have performed SEM of a nano composite for semi circular pellet in order to get surface morpology. But for what purposes we can do sample SEM at a crossection?

Hello Yaseen. Do you expect any spatial chemical variation inside your pellet? For instance, the cross-section SEM mapping might shed the light of the tendencies of the inner part concentrating certain elements. Though it depends on the size of your pellet, keep in mind the size of the beam and the area of influence.

If you are looking for surface properties, than observation of just a surface is OK. If you want to know structure of your pellet, you need to prepare cross section. For example, distribution of particles could be different on a surface and in a bulk material. In material sciences cross sections are very popular.

Dear sir@Vladimir Dusevich,

Thanks for your answer.

Dear sir in our case i check the surface morpholgy and particles distribution(i.e. EDX) Whether the nanoparticle is uniformaly distributed or not and whether the void/pores are reduced not. So what i need surface or crosection for SEM of pellets?

Well, you can do both collect the EDS map (if elemental composition is very) at surface and at the cross section and see what's the difference in the particle distribution.

If you expect to see morphological difference, then only SEM imaging at surface and at the cross section will work.

For best answer, is to you that figure out what's your objective and check the reference articles for the similar material and see how did fellow researchers have analyzed their sample, you will get more thorough idea.

You need cross section. If your particles are small, really "nano", then application of EDS could be problematic (spatial resolution is not good enough). Hopefully BSE could get better results. If your pores are not too small, then cross section should work. Beware of smaller voids - product of polighing could fill them. Use sonication. Alternatively you can try to fracture your specimen.