I just purchased a 2015 27" Retina iMac pretty much loaded, but got the super fast 500GB SSD drive because the 1TB is about $600 cdn more.
I got some xmas money so now I'm thinking of going for the 1TB drive, but thing is, I have to pack up the current iMac, send it back via UPS, wait for the refund from Apple, then re-order the new one and wait 2 weeks for delivery. Then there is the chance I could get a dud (maybe dead pixels or something else as it has happened to me before when I got 3 iMacs in 2012 that I had to return). Since I bought this before xmas I have until Jan 8 to return to Apple.
With OS installed out of 499 GB I have 464 GB free (with my music loaded in iTunes and some small apps).
I want to install PS, LR, Illustrator, Dreamweaver (CC 2015), possibly Office Suite, 3D rendering app, and usually have 1 game installed (20-50GB). I will keep all files for pics and video on an external drive. I would like to dual boot Windows, but apparently that can be done on an external Thunderbolt. Sadly a good Thunderbolt drive is about as much as the premium upgrade to a 1TB SSD internally.
Just trying to think "out loud" here to see what I come up with. I hate thinking about all the money I just spent on this computer to have to worry about managing disk space down the road.
My 10 yo Windows 7 PC has about 150 GB used on it's boot drive but I know programs are getting much bigger every year.