What are the benfits of a premium account?

While technically the only listed benefits are a 50% increase in silver and experience earned per battle that works out in real terms to a significant difference.

As a rule of thumb a premium account effectively doubles your silver income. This is because although it only increase your income by 50% your repair costs are not increased resulting in a much higher profit per battle.

The increased profit means that you will quickly earn the silver you need for the next tier and by the mid tiers have plenty left over to buy the crew training and modules that increase tank performance. Increased tank performance will result in a better win rate (unless you are lousy at tanks).

Likewise the increased experience will mean that you spend fewer battles with a stock tank and again improve your overall performance rating.

So a premium account does a lot more for you than just increase your income by 50%. It also increases your win rate.

+50% to earned XP and credits (link).

Earlier only player with premium account could made a platoon of three players and a company, but now it's not necessary (since version 8.5).

World of Tanks is Free2Play, not Pay2Win.

You gain silver and experience faster with a premium account.

When you get to higher tiers, you'll find it's very hard to make money in battles with a free account (around tier 6, I think, depending on how well you play and what tanks you play). (My chaffee is a level 5 light tank, and typically loses 5000 even with a premium account)

The 50% bonus increase to income means you make money until higher tiers. (No one makes money at tier 10, I believe).