I am a retired biology researcher and I believe that the most important is in the experiment itself. Then theory is useful to interpret the results of the experiment. When I began research one of my bosses believed that the only interesting experiments were first designed in the brain of the researcher. I do not agree. The most interesting results I obtained were serenpiditous results at the bench.
Unfortunately less famous than the discovery of penicilin by Fleming. But the principle is the same. Experimental results are generally not exactly what is expected and then good researchers are able to make new observations and this is often the most interesting because biology is so complex that no human brain is able to know everything. When I obtained my unexpected results I had talks with the most prestigious researchers of the time in this field. No one was able to give the good explanation. I got it only years later thanks to new results at the bench. This is at least my personnal experience.