Same target, the only catch is that you can’t both hit that target at the same time. Which would you prefer?
Would you, A, alternate the speed at which you both kick the ball, one slow one fast, or would you, B, control who kicks the ball first and second?
That’s essentially the same decision you make at an airport with intersecting runways, when you choose between using a command like “I’ll call your base” versus a speed command.
Due to the fact the runways intersect, each aircraft has the same target, the two runways that intersect. It’s your job in that scenario to control the pattern so those two aircraft don’t land simultaneously, remove any conflicts. Using commands like “I’ll call your base”, “extend downwind, or simply “turn base” without a “I’ll call your base” helps control the pattern. You ensure, like in option B, that one will be pretty much be guaranteed to reach the target before the other.
With speed commands, it’s more up to chance. And due to the fact that Tower can’t issue specific speed commands it’s even more of a 50/50. What is considered slowest practical in a TBM-930 is much slower then what would be considered in a B737.
Speed commands are an amazing tool but don’t rely too heavily on them to get the job done, in this scenario.