It is popular because you are not closed from seeing your physical drives. It is an active view of all your content. As you say a browser... of all image content.
Most of the time a "catalog" refers to a defined file that you decide to include a set of files, and THAT IS IT. In the catalog "manager all you will see are those files you decided to include.
Well that isn't managing much other than what you imported. The plus side to this type of catalog is portability of just those files in that catalog.
If you make 1 large catalog of all your images inclusive, this can cause the catalog to be slow. If corrupt it can effect all your images. It can also make your workflow more restrictive. Say you just did a shoot and you need to simply move files the fastest way possible off the cards or drive and you dont want to "ingest to a catalog using an application like LR. If you place those files on a drive you need to keep track of that. Now do that in a busy work environment or studio, and you can have yourself a mess.
Aside from all this, you are basically locking images into 1 application to start working from. Why? whats the gain? Also, you are forcing yourself to use the application as your only access point to your images. NOT SMART!
From experience, I would never lock my images to be accessed only via a catalog reader. You can ask why all you want, but 20+ of computing and imaging experience will tell you that you will regret it at some point. This is why I use LR as a cataloger in a Passive mode and only "ADD" images to the catalog. never move my actual files.
When you want to MANAGE your content, you want to see what is available to you, and then organize and catalog if you wish, or must, as in LR.
What is a DAM? How do you plan to use a DAM? What do I expect a DAM to do?....
Are some first questions you should ask yourself.
As far as ACDSee...It has a "default" database running in the background. You can also save and name your own databases. And according to the bolded text I read in the Help Content of ACDSee, it looks like it can.
I have worked in a multi location work environment for a number of years, and have yet needed to work with files "offline". Can you explain the purpose of this, or a common situation that you see needing by saying the term "offline" Maybe its the definition of "offline" that I need to clarify?
here is ACDSee's explanation....
"Cataloging Files in the Database
ACDSee automatically adds file information and thumbnails to the database as you browse. You can use the Catalog dialog box to add groups of files to the database without having to first browse the folders. This can be particularly useful when using ACDSee for the first time, and when browsing or managing large collections of images as it reduces the loading time required for these folders.
The first time you run ACDSee, you are prompted to catalog your files.
Exporting Database Information
You can use the ACD Database Export Wizard to save selected database information in a compressed format, and then store it as a backup, or share it with other ACDSee users. You can also choose to export your category and keyword definitions to a text file.
Exporting your database information differs from creating a backup in that you can choose to export only the parts of your database that you want to share or store with specific files, such as those on a CD. Other ACDSee users can import your information without affecting their existing database."