Wait until you lose a collar, call the Seiko boutique to buy another, and they tell you it they don't sell spare collars but can send the watch away for you instead. Luckily in the end they found a spare one and didn't even charge.
I just broke a link on an expensive watch over tightening a screw and a new link is £50. Pins and collars would have saved me.
Pro tip: when putting the pins back in put a bank card on a table/chest of drawers and force it back through. My wife still doesn't know what their weird little indents on one of the bedside drawers is.