Different but related concepts,
There are two basic questions:
How fast do you want it?
How much do you want?
For exothermic reactions you have to give one up in order to get the other one. As you increase the rate of the reaction by increasing the temperature, you are doing so at the expense of yield. You are making the product faster but you are making less of it.
Say for example a theoretical reaction
A <---> B and it is exothermic
at 10 C you get 30% yield of B and it takes two days to get that 30%.
you increase the temperature to 20C to speed up the reaction so that it only takes 1 day, however, that increase in temperature will make it so that your yield decreases to 15%.
A commecial example is the industrial production of ammonia using the Harber Process. The reaction is exothermic and it is ran at high pressures (usually between 500 atm and 1000 atm) and at high temperatures 500C. This high temp is costly in terms of the yield of NH3, however, for this process it ends up being better to get NH3 faster than to get more of it at a slower speed.