Let's take steak as an example.
What you are trying to do when you cook a steak either on a skillet, pan or bbq is cook it to your chosen degree of doneness. There are several problems and challenges that conspire to prevent this.
One is that the temp is difficult to guage even for experienced cooks even when assisted by a fast temperature probe. Secondly the steak will be cooked to different degrees throughout it's thickness. Thirdly the steak continues to cook whilst you rest it. Fouthly the cooking process causes the sinews to toughen so it toughens meat. etc etc.
What sous vide does is to gently cook your meat to exactly the right temperature to the degree and hold it there. It will hold it there for 24 hours if you wish and it will not detriorate. This means you are not cooking the accompniments to the time when the steak is perfect - because the steak will wait until everythign else is ready. This is really good when entertaining because the food is always ready whenever you want it to be.
When you "finish" the steak you put it into a searing skillet with butter/oil to caremelise the outside. Sous vide also has the effect of improving the meat so that (to my taste) it gives the steak of a softer wagyu consistency. You can't make poor meat good - but it really does seem to soften all steaks I've cooked - although I do prefer air developed rib-eye.
A side benefit is that the process by which you make meat safe to eat is a combination of time and temperature. This means that you can safely prepare chicken, turkey, pork etc to a more juicy consistency as long as you cook it (pasteurise it) for long enough. This is strange because you can safely eat pink chicken which is contra instinct!
No hard work or science cooking sous vide - the sous vide comes with very precise temperatures and minimum cooking times for every protein you will cook. Basically it means that all your proteins cooking will be better and consistently better - in other words your protein cooking will ALWAYS be perfect.
In terms of usage. I think it's important not to see it as an every day thing. Once the novely wears off - I do not use it all the time. I'll have weeks when it's not used and then a weekend where salmon will go in one day (absolutely perfect fish like you have never tasted) then steaks followed by a two or three day pork belly. The pork belly is finished under a grill to produce crackling and then painted with a honey, chilli, sugary spicey top and regrilled. So you end up with very juicy soft pork with a crispy skin with gorgeous soft fat. Something I find impossible any other way.
I'd say it's for serious cooks rather than the "everyday" kitchen.