So the No1 reason any of us buy posts is because others will click into them & comment. This increasing the impression on the post which bumps up or cashables.

A strategy that has worked for me on 1 post so far is saving up to buy a post that is used over & over again which can continue to give you rewards daily. 

The post I had owned for a few weeks was in another community which was a pinned post talking about whitelisting.

Obviously any new person that joined the group would read that post and anyone wanting to get whitelisted would read and comment on it so I found it a good investment.

So finding posts that are used over & over again are a great way to help you build your cashables in certain communities.