Elite cards are often op and sometimes essential for building a good deck. But you need to accumulate a lot of xps to unlock one and a lot of credits to buy a copy. But there are options to rent one for a limited number of plays. Since when you rent you get all three copies, it can make a lot of sense to rent the one you need for your deck.
For example, M5 Stuart, is an elite USA light tank, an essential card for all USA hqs. It costs 19000 xps to research and 86000 credits to buy ONE copy. But it costs only 26000 credits to rent THREE copies for 20 rounds of play, or 1300 per game. Since you earn about 9000 credits per game playing a T4 deck, you end up earning a nice profit if your deck contains only one rented elite card.
I therefore recommend new players to rent elite cards and grind non-elite cards first so you can relatively quickly accumulate more cards. And more cards = more options for building better decks.