It saves time in managing tags across multiple websites/domains where I work as an IT Manager for two schools - one K-12 public school district & private university (total of 5 campuses).
You need someone experienced at this, but it is well worth taking the training since there are some nuances involved when using these tools together! If you don't know what tag management software looks like or how they operate then do yourself favor by learning first. Save tons off hours of time spent manually editing each site separately.