I began my journey as a portrait photographer quite obsessed with the premise of blasting large studio strobes through giant modifiers. It was my workflow for years. In studio, I'd usually be washing my model with giant waves of light and on location I'd lug big, powerful strobes along with huge lengths of extension cords so that I could plug in and not bother with heavy battery packs. About a year and a half ago I stopped using my big strobes completely and eventually ended up selling them in favor of completely switching to small flash.
Small Flash Is More Convenient
I imagine this more or less goes without saying but lugging around big strobes is somewhat of an annoyance. It also means lugging around heavy stands and significant weight in sandbags to ensure that they don't topple over. My standard big strobe kit contained three strobes and rolled around in a large bag. My entire speedlight kit contains five lights and weighs less than even one of those original strobes.
Furthermore, my need for for assistance or running back and fourth to strobes to adjust light power has been replaced with a small commander unit on top of my camera which really isn't a feature that the big strobes offer until you edge into the higher priced range.
Small Flash Is Universal
Fairly early on I switched from Impact strobes to Alien Bees. That switch meant all of my modifiers were suddenly obsolete and needed to be repurchased. Meanwhile, speedlight modifiers generally require only a hot shoe. It doesn't matter if I'm rocking Nikon, Canon, Yungnuo, Godox, or any other brand of speedlight, my modifiers are all going to work just fine. This universality allows me to invest in a more diverse range of modifiers that I know will last until they wear out (years) and won't need to all be completely replaced if some other company comes out with a new ground breaking light that I feel compelled to buy.
Gelling Small Flash Is Much Easier
Of late, I find myself using more and more gels to add creative mood or even just to balance mixed lighting. Gelling a speedlight is much easier than trying to gel a large strobe. And with the the help of tools such as MagMod or the gel holders created by ExpoImaging, gelling has become even easier than before. Back when I primarily shot strobe I avoided gels as they added a giant headache to attach to the light, especially if I wanted to also modify the light with a softbox. Meanwhile, small flash empowers me to use gels with almost no effort.
Small Flash Is Cooler
A few years ago I was shooting a costume designer in a full suit of armor in studio blasting him with a set of three strobes. The armor was quite warm to begin with but with the help of the heat released by the big lights the set of armor quickly turned into a furnace. About halfway through the shoot I was worried that my model was going to face heatstroke. Even with the help of an air conditioning unit aimed directly at the model I often found that hot summers made for awfully uncomfortable shoots thanks to the heat generated by large lights. While small flash does create some heat the impact that it has on ambient temperature is trivial at best.
I loved my studio strobes while I had them and there is a certain magic to being able to fire away like a machine gun with full recharge in a second or two, but ultimately I decided that the benefits of small flash vastly out weighed the benefits of large studio heads in almost all situation. Thus, going forward, I have decided that if I do need tremendous flash power for a specific shoot I can always rent a set of large strobes, but for that vast majority of shoots my small flashes are certainly the way to go. Ultimately, moving to small flash has had no discernable impact on image quality which would have been the only factor that truly would have changed my mind. If you don't believe me head over to my Instagram and try to figure out exactly when I made the switch. Good luck.