Mongo DB performance when hosted on another server


I have my app running on now.js and using the free tier of mlab as an external mongodb. its a good setup for me when I wanted to get started writing code before anything else.

My app is getting closer to being released so I want to improve the server setup and see how the app performs in a ‘real’ production setup.

This might be a bit of a noob question but I am wondering since the mongo db url is accessed over the internet with a SAAS mongoDB provider that means it must just be so much slower than hosting on the server or within the network the server is running? I wanted to go with MUP but in the guide they recommend to have another mongo db server… but surely it should be on the same internal network?