You don´t need it, but the benefit is to have analytics data presented to you immediately in the back office of your WordPress installation instead of having to check in another tool like Google Analytics.

If you choose to use it, you don´t need a license.

I have it installed to check it out, and it works fine. The only annoying part is the pop-ups that ask you to go fo the paid version.

I don't find it to slow my website down at all. There I no change in both the speed metrics and the feel of surfing my website.

Bottom line, de-install if it isn´t of any interest to you, and use Google Analytics isntead.

Roy

You don't, but I'm curious - I've noticed a lot of people asking this question recently, what is it that's encouraging you to add it?

Hi, no you don't need to. The standard version suffices, so no upgrade or key required.

Monsterinsights just gives you what you already get from Google Analytics in the form of adding yet another plugin to slow your site down. Best advice is unless you have a really specific use for a plugin and by that not meaning it saves time but it makes things really better it is better to have less code for Google to have to read through and faster load times.