The trend these days on how to organize an individual workout session tends to lean towards Full Body training where you work upper and lower muscle groups on the same day. This is probably fueled by the DUP strategy that’s currently in vogue. The important thing to start off mentioning is that neither is better than the other. There are examples of extremely strong athletes both tested and untested that utilize both. They are simply a tool and certain tools are better in certain scenarios.
The split routine allows more focus on a particular area of the body. This means that on a given day your complete focus is either on the upper body, lower, or some given area of musculature. This allows you to utilize many more exercises and much more volume to target an area. You have more time and more energy to hit heavier weights on your main movement for the day and plenty of time for isolation/hypertrophy work to shore up the musculature. The downside is that you will have to use a lower frequency, out of necessity, which will mean you’ll need to use more volume during any single training session than you would if it was more spread out during the week with a higher frequency. A split then might not be best for someone new to the movements and looking to practice.
A split is superior when it comes to recovery. Because you have two or more days between training the same muscle groups there is ample time for soreness to dissipate and for energy to be restored. Contraste this with full body training where you might still be sore from the last session but you’ll still need to complete the training for the appropriate effect.
Full body and split training are both appropriate in various scenarios. We’ve talked about a few but there are many other situations. Just keep in mind both are tools.