Why it's so that at the time of cash out these fees and stuffs are deducted.Is it necessary?
Of course, its business, one way or another company needs something to support them. So it you are using a exchanges to trade and then withdraw them, you are deducted a certain fee to cover expenses like usage of their platform.
The fees are not that high though, compare to traditional banking system and it takes like a couple of minutes to a hour to see the funds going to your wallet. So to answer you yes, its necessary.
Nobody will offer free service, if you using any service you have to pay fee or commission or else how can that company will make revenue. Suppose if you do any transaction in the bank you have to pay service charge am I right? like that exchanges also collect a fee from you for your every transaction. to deposit, there is no fee in many exchanges but to withdraw you have to pay little amount.