Is it good practice to add remove table columns on the fly?

I think it's an acceptable solution if you want to create a functionality to manage data structures similar to streams (PyroCMS) or channels (EE). I am using this method if I restricted to RDBMS (MySQL), if I can use anything then a NOSQL (for example MongoDB or Cassandra) is a more viable solution because they don't require to use a fix data structure, every record (object) might store data with different structure.

@Narf mentioned PostgreSQL's JSON fields, this is a hybrid solution which can be a good choice too.

Oddly enough that is exactly what I'm trying to do, replicate ee's channels. But I've never ever restructured a table on the fly or even thought about doing so, but the more I got thinking about it, the more it made sense, and the more easier it seems to dump my data without doing complex joins and worrying about content fields being changed.

I wanna stick with mysql as it is by far the most common db in use. This is meant for the masses.

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