The numbers in the simplified form are smaller and so may be easier to comprehend. Also, working with the lowest terms means that the results of multiplications or divisions are smaller numbers and so less susceptible to errors - either calculation mistakes made by the user or rounding errors because computers can store and manipulate numbers to only a limited degree of accuracy.
33.3% as a ratio in lowest terms would be 1:3
1/5
1/5
14:9
17 and 4/25
Yes, they can.
Fractions and ratios sometimes need to be reduced to lower terms. Numbers never do. In fact, "lowest terms" is meaningless when you're talking about a number.
3 to 4 is the lowest terms of the ratios 6 to 8, 9 to 12 and 12 to 16.
In their lowest terms
33.3% as a ratio in lowest terms would be 1:3
9/10
1/5
1/5
1/5
It is 1413/5000 in its lowest terms
14:9
5/4