Issue polls are useful for two main reasons.
One reason is that they give politicians information about how much political space they have to support a bill. If people are lopsidedly against a proposal, then there’s a risk that your opponent in the next election will use that issue as a weapon against you. A politician who ran for office to pass what he thinks are good policies wouldn’t necessarily care about that, but a politician who ran with the goal of keeping the seat as long as possible has a reason to hew close to the polls. That’s your typical career politician – somebody who doesn’t really care about anything and just does whatever it takes to keep getting elected.
The other reason issue polls matter is that they are a tool for advocates to use to counter a lame Constituent Defense from a politician.
For example – Eric Evans and Bob Donchez would probably like to gesture to the 100 people who showed up to oppose the single hauler trash plan last night and say “See? My constituents clearly oppose this plan, so I can’t vote for it.”
The poll is useful because it shows that’s wrong, and actually a much larger random sample of over 1500 of their constituents is lopsidedly in support of the plan.
Eric Evans and Bob Donchez cannot point at the 100 people and claim that the politics says they can’t vote for single hauler. We have heard from many many more people than that, and the group that turned out is actually not representative of what most people want.