This depends on two factors. The first and probably most important factor is what the course you are doing will be marked in. If it is marked every kilometer then it is a good idea to know how fast you should be running each kilometer. If it is measured in miles then you should know how fast you are running each mile. Sometimes marathons are marked every five kilometers in which case it is important t know these splits as well.
The second is what measure you are comfortable with. If you are from the USA you may be more comfortable knowing your pace in miles and if you are from most other countries kilometers will be familiar to you.
Posted in: Goal Times and Effort