Some people has a predisposition to ear infections. I am one of those. Ear drops are preventive maintenance in my case.
I have had 10-15 ear infections over the past 35 years after scuba or skin diving. Once they get going it is very, very painful, requires a doctors appointment and antibiotic ear drops with no diving for several days. Can really screw up your vacation. I am now 60% deaf in one ear and 35% in the other. I believe a significant part of this hear loss was due to ear infections, although some is probably due to age.
I now use prepared swimmers ear drops, alcohol with a little bit if glycerin to replace the protective coating of lost wax. A few drops in either ear and no post dive infections. No negative side effects. Cost is pennies per dive.
In a pinch, when I forgot to pack drops and have felt the beginning of an infection, I use straight denatured alcohol out of a 16oz bottle, it is also effective, but drying.