Question: Is it necessary to soak rice every time before cooking.What happens if you don't soak rice? Does it effect the taste after cooking? If soaking is necessary then, How much time is required to soak rice?

Answer: 
*Rinsing* the rice is always suggested, it removes the leftover husk, powder from the rice being handled and/or processed, **insect fragments** (you'd be amazed!) and more.

*Soaking* the rice is part of the cooking process. Wild and brown rice benefit from this because they'll more evenly cook '*to the tooth* (al dente)' with less liquid and time; this is how you get a nice and fluffy pilaf. If you don't soak the rice before cooking, it will require more liquid and time, and be more likely to come out clumpy and overcooked.

Most good markets have *dozens* of kinds of rice and each one does best with a different kind of process and finesse. And we haven't even talked about Sushi rice or Arborio (literally: "absorbent") rice yet. 

Soaking long-grain or basmati rice has benefits too, depending on how you season it. If you like to cook your rice with *achiote* powder and safflower strands, soaking in some warm water for an hour is really helpful. 

Some South East Asian recipes call for the *liquid* where rice was soaked for a few hours as a thickener or ad-hoc liaison. *Tinola* (a brothy chicken dish) is one, *sinigang na baboy* (sour pork soup) another. A fan of either dish can tell when the broth is missing that starchy quality only rice can bring. Rice flour, or cornstarch, even in small amounts, would be too much.

So. `tl;dr;`:

* *Always* wash whole rice for hygienic purposes.
* Consider soaking the rice as part of the technique of cooking it, but make sure it's a conscious decision, e.g. "I think soaking it will yield [result]"
* Pre-packaged parboiled rice usually doesn't need to be washed *or* soaked, follow the packager's directions and your own instincts / experience.
I assume you’re not mixing the terms rinsing and soaking:

Rinsing is for geting rid of excess starch on the surface of the rice. This way it won’t be sticky or be less sticky.

Soaking rice does two things:

1. It will, hydrate the rice grains; thus they will cook slightly faster (dry rice also cooks pretty fast)
2. You extract the surface starches into the soaking water. if you discard the soaking water, it will have similar effects to rinsing the rice.