Not just time, space and ease of shipping as well. After being in this game for two years as a seller, I've been looking at my data more closely this year to really focus on the money makers taking into consideration various factors. I found that I used my heart and gut feel more than hard numbers in the past.
I'm now at the stage where I've had enough time to 'age' good number of sets and would like to be more selective on the sets I buy moving forward to focus on winning themes. Where I live, star wars, Technic, Harry Potter, creator expert, speed champs continue to be top performing themes. Architecture, Brickheadz and Ideas have good returns but volume is way too low. I tried going into Minecraft and Friends but it didn't really work out.