Cons of having one big level instead of many levels?

[piotr]

I'm planning a side scrolling platformer and I was wondering: 

1. what are the cons of having one big level instead of having the game split in many levels?
2. what are the limits of phaser, if any, regarding such solution (e.g. is there a maximum size for a tilemap)?
3. are there any optimizations that could be put in place to achieve that (e.g. triggers to load enemies and items only when needed)?

Thanks

p.