This question has been bothering me for some time, esp. after procrastinating in forums while trying to decide what expensive gear is eventually "worth it" to me :-) ... please not I'm not trolling and applaud everyone who puts his/her money into expensive gear to get shots just for the sake of remembering his/her kids or such
So here it goes: When looking at a lot of sample shots, I'm wondering "would have that gear been necessary", and the inverse question "What shots can *only* be taken with this kind of equipment" and why is an expensive dlsr necessary at all?
My guess is that a good part of the dslr market segment is populated by 30-40+ year old males who made their first photographic good experiences with analog dslrs (me, too). They just stick to the good ol' ways while the companies know these customers are rather well off by now and will respond to "quality" and "feature" upselling, so they exploit these suckers pushing the next $3500 camera or $2000 lens to customers who feel secure when having expensive gear.
I think I'm not alone with this question, and the difficulty often results in pro photogs either recommending "just get a [enter latest model name here], you'll never regret it" or the exact opposite "no need for the latest equipment". So here is my list that a dslr with proper equipment is good at, i.e. as a pro shooter you are well advised to take it into consideration or you'll end up being asked "My grandma could have shot that with her p&s"...
- lighting: multiple off-camera flashes that are reliably triggered with fast x-sync or hss give a distinct "non-p&s" impression
- thin depth of field and/or strong bokeh: can only be done with expensive lenses with large glass elements, and esp. fast primes
- shooting reliability, i.e. more "keepers": while you can take good shots with nearly every equipment, it is seldom or never known how many shots or opportunities were lost. This concerns button layout, af precision, ...
- shooting moving objects: pro dslrs are faster, at least at the moment. That concerns af speed/tracking, shutter release time and fps - the latter being better on mirrorless.
- shooting in extreme natural conditions: pro dlsr equipment is sealed and sturdy, but for many usages throw-away equiment might make more sense and outodoor/underwater p&s will be there sooner or later.
- shooting in difficult lighing conditions: the best sensors will always be the most expensive and eventually end up in dlsr equipment, meaning more dynamic range (well, with Nikon :-)) and higher iso capability for faster shutter speeds or low light shooting
- (super)tele shots: longer focal lenght with decent quality is and will be a domain of expensive equipment
- sharpness for large prints: while the next iPhone will probably have more mp than the current Canon crop cameras, attaching a $1000+ lens will still make a difference.
- composition: a large ff viewfinder enables you to concentrate on the shot, at least as long as there are no dencent electronic viewfinders for p&s around
... added, though imho only slightly valid because a eos-m takes ef lenses, too:
- macro capability: true 1:1 (or higher), not just 'close focusing' as 'macro' has come to mean in the P&S world
- tilt-shift lenses: ability to correct for perspective distortion, and manipulate the DoF/plane of focus in a way other that a uniform linear distance from the camera
Let me know if anything else comes to your mind what's the sense of buying a dlsr system.