There is a difference if the exercise is approached by the time versus the distance. It’s not only training factors that makes difference, but also psychological factors. Depending on the exercises time-based training can be either easier or harder than distance-based. Some runners favour more the other exercise style, but you should mix these both.
Time-based running can ease the pressure to cover some distance as fast as you can. It’s more effort focused and suit also perfectly to tempo runs. As you need to listen to more your body and how you feel during the running. During the intervals, runners tend to run more even pace when using a time-based approach.
Use time-based training for easy runs, tempo, speed training when you are looking for even pace. Don’t base all your training for this style, as it might be difficult when training for the race.
Distance-based training is excellent for long runs, especially if you are training for a race. It’s also a good way to practice pacing and overall racing. During the speed training, runners tend to run a faster pace, as there is psychological pressure to be as fast as possible at a certain distance. This also can lead to difficulties to run an easy pace.
Running distance-base can make you a number slave when it’s difficult to relax and you just compare all your exercises to each other. Use distance-based training to fast exercises, pacing practice and long runs.
The best results are gained by mixing both and making clear differences between these styles. It’s not wrong to use only distance-based or time-based training, but mixing can give more variance and make even more progress. They both also challenge the mind differently.