It is not only homeless, people with very low pensions or not able to get a proper full time job also hunt for them, everywhere.

On the streets, trains, subway, beach, lakes, you name it.

To the point that many people don't throw away bottles anymore, leaving them grouped outside the trash cans, as means to help those people pick them without messing with trash.

There are even trash cans in the Rhein region that have bottle holders around them.

So yeah it helps keep the street clean from bottles, but fighting the causes of this 2nd level economy would probably be a better idea.