Minecraft has a lot of bugs or otherwise surprising behaviours that parts of the community have come to rely upon. This means that most non-vanilla minecraft servers aren't 100% drop in replacements. You have to make a decision what behaviours you want vs the performance and simplicity gains you will gain.
For example there there are tricks that allow you to delete bedrock blocks. Which then lets you either get onto the roof of the nether, or drop below the bottom of the world. Not all of these tricks will then work depending upon the specific minecraft server.
Another example is that in vanilla you can "bomb" people with experience orbs, the sheer number of orbs on the screen will grind their game to a halt since there are too many objects to track and render. Some minecraft servers work around this by grouping up experience orbs into a single bigger orb. That way you have fewer orbs on screen at once.