TTL & Being WiredPortable flashes have the benefit of optional TTL (through-the-lens) control. These flashes work in conjunction with DSLRs to read the amount of light reflecting off the subject and terminate the flash output at the appropriate moment. Strobe manufacturers, who for years produced equipment that required manual control, are starting to incorporate their own remote controls for triggering and output adjustment, as well as actual wireless TTL connectivity.
Speaking of connectivity, another benefit of small flashes is their compact size, low cost and battery power. Studio strobes can simply be plugged into an AC outlet and run indefinitely, but the ability to shun AC power and produce bright light in even remote locations gives portable flashes—and even battery-powered strobe systems—a distinct advantage. Pack-and-head systems allow you to plug in a single electrical outlet and power multiple lights—often, up to six or more heads from a single pack—while monolights are each powered individually. For working across great distances, a handful of monolights can be spread out as far as there's electricity to reach them.
Because strobes have long been the de facto standard, there are tons of modifiers and accessories available for everything from small flashes to studio strobes. A single softbox can work with a variety of different brands and configurations with just the change of a speedring or mounting bracket.
Power: You Get What You Pay ForCompared to entry-level continuous light sources, strobes can be fairly expensive. But when you factor in the amount of light they deliver, the power-to-price ratio of all but the costliest studio strobes is favorable. Strobes and flashes can also improve the appearance of sharpness; because longer exposures aren't necessary and because strobe durations are so short, they eliminate all but the most egregious camera shake and subject movement.
Strobes and flashes can also do something no other light source can do: Because of those extremely short durations (often, 1/1000th of a second and much faster), strobes can freeze fast action and allow the ambient exposure to be adjusted independently of the strobe exposure in the same click of the shutter. Adjusting the shutter speed from 1/60th to 1/125th has no effect on a strobe with a duration of 1/2000th, but it sure will change the ambient exposure. This opens up a whole world of creative possibilities no continuous light can replicate.