Check out the Solo vs Pool article to learn more about the difference between Solo and Pool mining.
Not everybody should use the same pool.
If a pool dominates (controls at least 51% of all the mining power), it means that they have full control over the blockchain and can therefore cheat the system by modifying some of the values (essentially creating, stealing, or removing money). As a result, pool diversity is very important and people should try to find the best pool or independent ones, to solidify the network.
If you are a pool owner and wish to add your pool, just create a Pull Request (or message me @Pandawan#4158).
Since this is a pool, you will most likely get paid 100 blocks after the blocks that you have helped mine.
For example, if you have mined block 1000, then you will get paid by the pool when block 1100 is mined.
You can check out which block have been mined on the Explorer.