Studio flash vs. speedlights

PROs and CONs of speedlight vs. studio strobe

Pro speedlight:
Very portable, no reliance on AC outlet
ETTL or Auto flash exposure control
Minimal setup time on location
Very rapid light output, typically 1/1000 - 1/10000

Pro studio strobe:
Higher light output than speedlight
Modelling light lets you immediately SEE the effect of setup, without taking a shot
Many light modifiers available (umbrella, softboxes, snoots, grids, barndoors)
Radid recycle, typically <1 sec.
Unlimited flashes (wall power)

Con speedlight:
Slow recycle from full output, without supplemental expensive battery packs
No ability to see affect of lighting setup without taking a shot
Need to transfer photo to a computer to see image at full size to assess lighting
Fewer available light modifiers (umbrellas, minisoftbox)

Con studio strobe:
Always have to find AC outlets
Slower to set up on location
More cables (AC) to trip over
No ETTL control, no Auto flash; manual only
Need separate flashmeter for efficiency of setup

That's a very nice synopsis, Wilt.

To put the power aspect into perspective, here are the readings I got using a Speedlite vs. an Alienbees B800 strobe, shooting into a silver umbrella and measured at a distance of 9 feet from the umbrella:
B800 full power: f/13
580EX II full power: f/4.5

That's a difference of three stops. That means it would take eight 580EX II Speedlites to equal the output of one B800 strobe. Speedlites are remarkably efficient when used direct, because of the reflector and fresnel lens that concentrates the light where it's needed. But any sort of diffuser or modifier throws this efficiency out the window.

This doesn't mean that a Speedlite won't do the job. But it depends on the job. For three out of the last four portrait shoots I did, I used Speedlites because of the portability and ease of setup advantages that Wilt mentioned. But they were single portraits so I could put the light very close to my subject, and I was dealing with adults with the patience to wait for the units to recycle. Not every job gives us these luxuries.

There's also the matter of remote firing.

Speedlites need another Speedlite or ST-E2 for wireless, Off-Camera Shoe Cord for wired as far as Canon solutions. There are also third-party solutions, but can be flaky (such as optical triggers not working on Speedlites). The 580EX-II now features a PC sync socket, opening up other means. You can use hotshoe adapters also.

Studio strobes require a PC sync cable or radio trigger (such as Pocket Wizards, Einchrom Skyports or other third-party). Many have built-in optical triggers at least.