The whole process of polishing has undegone a number of changes. The original limit was ten per user, including yourself. Only having someone blocked would prevent polishing.
Spring 2015, this was first changed to 100 per user, then the ability to limit who can polish and be able to change that at will. The latest change came inthe Summer of 2015 and it's based on level. At my level 63, it's 1,000 per user per day.
People would get blocked just for polishing someone's pony. The problem is, blocking should really only be used for obnoxious members who wear out their welcome or should probably be reported. Keeping someone blocked for more than three days, to just make a point, in my opinion, is childish, yet some still have me blocked years later.
When it comes to polishing someone's bling, people are more likely to complain about it being blocked if they either don't have much, or they haven't given out much. Some people have a lot of bling, many of them traded so that means they also bought a lot of bling. That means that they're a big part of what keeps this site running. So while I might not like it if someone blocks their bling from polishing, I understand it, and respect it.
The Mega Polisher doesn't create an unlimited amount of polishes, rather it increases the limit you may polish for one user at 5,000. It was nearly essential before the changes to complete the 10,000 polishes in one day achievement, but with 1000, you only need it if you want to get more points, so if that's what you really want or need, which I did when I needed 5 billion points in a day achievement to get my crown at level 63, because altruizing, 2X running bombs and points boosts weren't going to be enough. I barely made it.
The two times to run a polisher are as follows
1. If you want to get good points when the bonus is for polishing or for all powerups. The person who owns the bling you polish AND the person who gifted the bling you polish all get bonus points when you use a polisher.
2. If you want to polish a LOT of bling in a day, I advise you to first polish all you can based on your daily limit. THEN if you have the energy to continue, run a polisher to get the 10K in one day or as some of my friends and I did, polish 10K or more Limited Edition in one day.