@Natalia Perlova as an investor and agent (investor first) I can say it's not needed. If your plan is to buy and hold and not pursue some form of real estate as your primary job (Property manager, appraiser, realtor ect) then just hire a good investor friendly agent. As you may know, the buying broker does not get paid by you the buyer but rather the seller, so it's 'free' to hire an agent to represent you when buying property. If you plan on flipping property or looking to make RE a full time thing, I would lean towards getting it.
As others have said, it costs a few thousand a year so you should be somewhat active either selling your own property or representing others to justify the fees. Keep in mind that once you are an agent you are bound by certain ethics when going under contract ect. For example, wholesaling while legal in many states is one of those 'grey' areas that as a realtor I probably wouldn't do. Buying property off market... are you going to loop your broker in on that or not tell them? Also keep in mind, that yes you will save money selling your own properties but your broker will still have you 'split' a certain % with them.
For example, you sell your house for $300k. Typically you would spend roughly 5% in listing fees... say $15,000. Of the $15,000 1/2 goes to the buyer broker. So essentially you would be saving yourself $7,500 dollars... not bad. However, after your split with the broker... this could be anywhere from 50/50 split to 90/10 split your $7,500 can quickly dwindle down. Then of course there is taxes you have to account for. My point being, if you choose to go the Re license route, be sure you are doing enough transactions to cover the yearly fees and shop around with different brokers.