The pool "talks" to you every 30s (at least) to give you new work.
Keeping your average share rate more active than that is advisable since you have a better chance of finding out about a disconnect sooner.
Personally I'd not put the average share rate less often than every 5s.
Remember that the same statistics apply to shares as to blocks.
A 800%+ Diff block on a pool is rare, but expected to happen 1 in every 2981 blocks.
Same for shares, you'd expect one to show up 8+ times slower than the expected value, 1 in every 2981 shares.
That's not a lot of shares ...
A simple CDF table to refer to:
0.86466471676339 200.000% 1 in 7.4
0.95021293163214 300.000% 1 in 20.1
0.98168436111127 400.000% 1 in 54.6
0.99326205300091 500.000% 1 in 148.4
0.99752124782333 600.000% 1 in 403.4
0.99872735771441 666.666% 1 in 785.8
0.99908811803445 700.000% 1 in 1096.6
0.99966453737210 800.000% 1 in 2981.0
0.99987659019591 900.000% 1 in 8103.1
So if you have it set to expect 1 share every minute, then you'd actually expect on average to have one in every 7.4 shares taking 2min (200%) or longer, and one in every 148.4 shares taking 5min (500%) or longer.