What does op-permission-level do?

In the new server.properties file, there is a line called op-permission-level, which is set to 4 by default. What does it do?

According to the Minecraft Wiki:

Sets permission level for ops.

Each level grants additional privileges over previous (lower levels)

1. Ops can bypass spawn protection. No commands are assigned for this level.
2. Ops can use /clear, /difficulty, /effect, /gamemode, /gamerule, /give, /summon, /setblock and /tp, and can edit command blocks. (Single player cheating)
3. Ops can use /ban, /deop, /whitelist, /kick, and /op. (Multiplayer management)
4. Ops can use /stop, /save, /save-all. (Server management)

4 is the highest OP level, and a level 4 operator can use all the commands from levels 1 to 3.

As said in the comments, for small servers, you probably want to your ops to be level 3.