It is for shared hosting. 'a long time ago' we used php-fpm but switched to fastcgi because it was easier for write rights and see who was running scripts using top-command.
But this was a long time ago, so maybe it is evolved and there are better solutions.
Depends on what you call small.
We had mod_php with mod_ruid2 running on a server with 60-70 customers until last year, works great, also for security.
You don't have to worry about rights because as with php-fpm scripts are run as the user. Downside is you can only have 1 version of php running officially when using mod_php with mod_ruid2.
So this way you can also see which user is running scripts with the top command.
Php-fpm is great for giving your user a change to choose which php version they will use. Als this way they can easily test if their scripts work with a new version, before you stop supporting a certain version.
They all have their benefits and downsides, depending on what you want to use it for.