carroters has covered a lot of the reasons.But also .....1/3 pot bet here would be 30 cents ......it will fold out some hands that beat you such as 2pair , possible trip 8's etc as they'll put you on a J and the straight. if they raise you , its an easy fold and you have saved 30 cents compared to the amount you were willing to check call and there will be some people dumb enough to call with worse anyway who might have checked behind.