Up to this point when preparing steaks, ribs, or any sort of "meat" I would apply my spices in sequence: first adding salts, followed by a pepper-based powders, and lastly some sugars (if applicable). I often see cooks combine these spices into a bowl to make a rub. Is there any advantage to doing the latter?
An additional factor is prep time. You can make a large batch of spice mix quickly, spooning tablespoons rather than quarter teaspoons and then it's made ready for many portions. Dry mixes keep as well as unmixed spices so you really can make big batches even if you don't get through it very fast.
Another advantage: it helps prevent contamination of the larger containers of spices.
You don't want to get raw meat in to your larger containers of spices, or coat your pepper grinder with it, etc. This is especially important in professional kitchens where you might be required to discard the big container if it happens (and even if its safe, do you want raw meat juice splashed in your salt or sugar?). You can of course (if you're careful) use one hand picking up measuring spoons, scooping, pouring and the other for any handling of the meat, but it's easier (and far less error prone) to just measure out the amount you need first. And at least my pepper grinder requires two hands. Same with many spice grinders and most (all?) mortar and pestle sets.
So, you could measure each spice into different small bowls or ramekins. Sometimes you do—like if you're going to put salt and pepper on something by sight, not by careful measuring. Or if they're being added at different times in the prep.
Otherwise, it's easier to use one bowl. Fewer dishes to wash! And that means you've made a spice mixture.