Are low sample studies redundant most of the time? Are low sample studies redundant most of the time?
Should all studies have large sample sizes?
OTOH the low sample is sometimes an always present thing. Millions of people cannot be easily studied.

The sample size needed is entirely dependent on the signal:noise ratio and the degree of experimental control.  One dietary study with 24 patients put in a metabolic chamber for one week, with precise measurements and using a crossover design provided more information than a 10,000 person observational dietary study.
There are ways to compute sample sizes needed for model reliability, as a function of the signal:noise ratio (e.g. true $R^2$).  See this.
