Caveats of loading Marketo Munchkin via a Tag Manager
Most users would know Marketo’s custom JavaScript tracking code, called Munchkin, which tracks all people (known or anonymous) who visit your website so you can react to their visits with automated marketing campaigns (this applies to only known people in the database, though).
I see a significant number of users loading Munchkin JS via a tag management system (e.g., Google Tag Manager) without knowing that this adds another level of asynchronous loading to their webpage.
In other words, the tag manager JS is first loaded asynchronously, and then it loads all the tags asynchronously (i.e., 2 async calls for loading JS injected via a tag manager).
Due to this additional header of async loading, there could be a case where the Munchkin JS may not have sufficient time to load and send a hit to Marketo in case a visitor quickly navigates away from the webpage.
Don't get me wrong here, most tag managers are super-fast, and the chances of this happening are pretty slim, but it can't possibly be faster than loading Munchkin on its own, since you're technically loading another script over the network first.