Originally Posted by
The Weak Link
If your tool is like mine, it provides some tension on the links
^^^ This.
Just ask someone who has just replaced a cassette, RD pulley wheels, and a middle chainring because he used, but ignored his chain checker.
Chains are cheaper.
I know that since you have to string several together, chains aren't as cheap for bents, so it throws the whole chains are cheaper than gears equation into a tizzy. But you also use eight or nine-speed chains which are a whole lot cheaper than 10-speed ones. You can buy three 8-speed chains for what one of my 10-speed chains costs.