I follow the changes made in the East Yorkshire area. Andy Ayre created a twitter feed for the area which generates tweets as osmeastriding. AndrewArm creates an RSS feed for the area too. Then there is the ITOWorld tool which is helps me look at the editors for a selected area.
Andy Ayre's twitter feed is based on a rectangle that encloses the county, so it also includes York, part of North Yorkshire and part of northern Lincolnshire too. It is very quick so edits appear only a few minutes after they were made and I check it every day. Andy's algorithm looks for changesets that fall within the rectangle, so big changesets that span the county are ignored whether objects in the county are edited or not.
AndrewArm's RSS feed is based on the polygon that describes the county and so it is more focussed. It is up to a day behind the edit. It does, however, show any edits in the county, including changesets that cover bigger areas than the county, so-called big edits.
ITOWorld's system will be familiar to many. It allows you to choose a rectangle to monitor and provides an RSS feed for changes in the selected area. This is a day or two behind the edits and the size of rectangle is limited and is much smaller than the size of East Yorkshire.
Monitoring an area reveals new mappers. Once they have made a few edits I usually send them a message saying 'Hi' and offering info or help. Newbies often want to check something or ask how to do something.
Monitoring also shows up vandalism. Speedy action means vandalism can be reverted without much risk. Reverting a vandal's edit means he may be dissuaded from doing it again, but at least the harm is limited.
Another thing that monitoring shows up are mass edits. Recently there seems to be a spate of them and some are harmful and annoying. When someone replaces a misspelt tag that is helpful. Changing Name=* to name=* or buildng=yes to building=yes would both benefit the object. However that is not what many mass edits are about. Some seem to be about homogenising the data, replacing the value part of tags with something generic. Sometimes a tag is removed and a replacement tag is added in its place.
I challenge the people who fire off these homogenising edits, which I dislike. The commonest excuse is that the wiki says the tag should be like this. This is infuriating. The wiki is full of controversy with edits chopping and changing the meaning of a tag back and forth. The open part of OpenStreetMap can be interpreted in many ways, and one way is that the tags that are used are open, that is any tag key and value is allowed. I also hear that TagInfo shows that value x is the most popular so every object must be changed to x. What TagInfo actually shows is that there are many uses of the key and that x is not the only way to use the tag, so why should they all be forced to be the same?
The second reason quoted is that how can the data be used if it is not consistent. Ontologies are mentioned. The odd thing is that people who say this are not the people who use the data for rendering, routing, analysis or whatever. The OSM data as derived from the API as XML (or pbf) needs to be processed to be used. That processing often loads the raw data into a database or processes it into a working file and that loading process can include catching a range of values that are useful for the render, analysis or whatever. If the variations of the key values are useful then they are used, but if some mass edit has flattened out the data into a monotonous grey, then those differences are not available. This processing will be a few lines of code, written once and used over and over without harming the detail at all. This is how landuse=cemetery and amenity=graveyard can be treated as the same thing or treated differently.
I know that a carefully chosen tag that gets splatted into some other meaning by a thoughtless mass edit is annoying. If that annoyance persuades a mapper to stop contributing to OSM that is a problem. Our most precious resource are our mappers and if a mass edit risks losing just one of them then that is a very serious indeed.
I have been accused of not wanting objects I created being changed; of being too protective. I'm not and that misses the point: OSM is a wiki. The objects are all open to edit every day. I just want those edits to improve the quality not squash it out.