Yes, I will probably convert 132511/43 into a FP approximate value only if I need it as a human to estimate the magnitude, but not if my aim is to store the value in a computer and if I am given the technical means to store it as a rational.
The trouble with rationals is that the denominators keep growing. If you add 132511/43 and 27/67 and 1024/853, you've got 7577076638/2457493. Pretty soon you'll hit Perl6's built-in limit of 64 bits in the denominator, and it will switch to binary floating point automatically. Rationals do not solve the problem, but they do make things a lot more complicated.
(Yes, I'm aware that you can sometimes cancel out common factors between the numerator and denominator. No, this does not solve your problem.)