People are interested in computing the zeros of $\zeta(s)$ and related functions not only as numerical support for RH. Going beyond RH, there are conjectures about the vertical distribution of the nontrivial zeros (after "unfolding" them to have average spacing 1, assuming they are on a vertical line to begin with).

Odlyzko found striking numerical support for such conjectures by making calculations with zeros *very* high up the critical line: hundreds of millions of zeros around the $10^{20}$-th zero. See the Katz--Sarnak article here and look at the picture on the second and fourth pages. These vertical distribution conjectures do not look convincing by working with low-lying zeros.

If you're not interested in considering large-scale statistics of the zero locations, there is a small refinement of RH worth keeping in mind since the calculations supporting RH are based on it: the (nontrivial) zeros of $\zeta(s)$ are expected to be *simple* zeros. This has always turned out to be the case in numerical work, and the methods used to confirm all zeros in a region lie *exactly* on -- not just nearby -- the critical line would not work in their current form if a multiple zero were found. The existence of a multiple zero on the critical line would of course not violate RH, but if anyone did detect one because a zero-counting process doesn't work out (say, suggesting there's a double zero somewhere high up the critical line), I don't know if there is an algorithm waiting in the wings that could be used to prove a double zero exists if a computer suggests a possible location. I think it is more realistic to expect a computer to detect a multiple zero than to detect a counterexample to RH. Of course I really don't expect a computer to detect either such phenomena, but if I had to choose between them...

From Wikipedia's table on its RH page, the latest *exhaustive* numerical checks on RH (all zeros up to some height) go up to around the $10^{13}$-th zero. There are other conjectures that have been tested numerically far beyond $10^{13}$ data points, e.g., the $3x+1$ problem has been checked for all positive integers up to $80 \cdot 2^{60} \approx 10^{19}$, Goldbach's conjecture has been checked for the first $2 \cdot 10^{18}$ even numbers greater than $2$, and the number of twin prime pairs found so far is over $8\cdot 10^{14}$. With such examples in mind, I would not agree that the numerical testing of RH is out of line with how far people are willing to let their computers run to test other open problems.

thatmany papers. $\endgroup$ – Nell Mar 21 '19 at 14:24