You bet for value.
Part of it is value from the chance of winning a showdown.
Part of it is value from the chance of winning without a showdown.
Part of it is value from knowing what he has.

The value of knowing what he has is only present if it helps you win more at showdown or win more often without showdown. USUALLY the value of knowing what he has is...
1) not great enough to justify putting money in for information alone - it is an anxilliary reason for betting at best. It's wisest in almost all cases to attribute the value of information as 0 when you calculate your EV
2) overestimated - one action from him can mean more than one thing - so you put money in to get information and the information you get can mean multiple things - not such a great deal
3) sometimes wrong - through you being leveled or leveling yourself the information that you pay dearly for may in fact cause you to lose showdown value or get him to fold less often, because the adjustment you make is either the wrong one for the information or the wrong one for the actual state of affairs that the information you paid for does not correctly reflect.