NL Hold Em was traditionally played with an ante before online poker. If you look at the game in theory, the amount of hands you should play overall is very low because the single SB and BB aren't enough to justify getting involved much, especially from early positions.
In practice, people play as if there are invisible antes. And better indicators of whether an ante is necessary in a cash game are things like standard open sizes and how often pots go multiway pre flop.
The reason for an ante is simple though, to drive action. If people don't open their stealinh ranges up to try and pick up that ante, they will lose a ton of EV while the person that does open up rakes in a ton of free money. In general, people don't actual open bigger when an ante is involved. And that because from my experience, people don't adjust their defending and 3 betting ranges against people attacking the ante. If players fold the same among to a person opening to 3x even when an ante is involved, then that person is just going to crush everyone. They are risking 3 to win 2.5 (assuming a standard BBA). They only need to successfully steal 54.5% of the time to show a profit.
I'm modern tournaments is even crazier. People routinely in later stages open to the minimum. Risking 2 to win 2.5. That's just 44.4% success rate needed to turn an in immediate profit. If you've watched any of the high rollers, you know how tight they are playing due to ICM concerns. Imagine the was no ante and they could survive even longer if they only had to put in 1.5bb per orbit instead of 2.5bb. The tight play would be magnified.
Long story short, ante in low stakes (up to 2/5 and maybe 5/10) isn't really necessary because people play looser than they should. Which incentives winning players to attack that loose play. But when everyone is aware of correct ranges with no antes, the have can be very nitty. So an ante helps that. So do Stand up game, straddles, 2-7 bounty, etc.
