What makes TortoiseSVN such a good Subversion client? Here's a short list of features.
TortoiseSVN integrates seamlessly into the Windows shell (i.e. the explorer). This means you can keep working with the tools you're already familiar with. And you do not have to change into a different application each time you need functions of the version control!
And you are not even forced to use the Windows Explorer. TortoiseSVN's context menus work in many other file managers, and in the File/Open dialog which is common to most standard Windows applications. You should, however, bear in mind that TortoiseSVN is intentionally developed as extension for the Windows Explorer. Thus it is possible that in other applications the integration is not as complete and e.g. the icon overlays may not be shown.
The status of every versioned file and folder is indicated by small overlay icons. That way you can see right away what the status of your working copy is.
All Subversion commands are available from the explorer context menu. TortoiseSVN adds its own submenu there.
Since TortoiseSVN is a Subversion client, we would also like to show you some of the features of Subversion itself:
CVS only tracks the history of individual files, but Subversion implements a “virtual” versioned filesystem that tracks changes to whole directory trees over time. Files and directories are versioned. As a result, there are real client-side move and copy commands that operate on files and directories.
A commit either goes into the repository completely, or not at all. This allows developers to construct and commit changes as logical chunks.
Each file and directory has an invisible set of “properties” attached. You can invent and store any arbitrary key/value pairs you wish. Properties are versioned over time, just like file contents.
Subversion has an abstracted notion of repository access, making it easy for people to implement new network mechanisms. Subversion's “advanced” network server is a module for the Apache web server, which speaks a variant of HTTP called WebDAV/DeltaV. This gives Subversion a big advantage in stability and interoperability, and provides various key features for free: authentication, authorization, wire compression, and repository browsing, for example. A smaller, standalone Subversion server process is also available. This server speaks a custom protocol which can be easily tunneled over ssh.
Subversion expresses file differences using a binary differencing algorithm, which works identically on both text (human-readable) and binary (human-unreadable) files. Both types of files are stored equally compressed in the repository, and differences are transmitted in both directions across the network.
The cost of branching and tagging need not be proportional to the project size. Subversion creates branches and tags by simply copying the project, using a mechanism similar to a hard-link. Thus these operations take only a very small, constant amount of time, and very little space in the repository.
Subversion has no historical baggage; it is implemented as a collection of shared C libraries with well-defined APIs. This makes Subversion extremely maintainable and usable by other applications and languages.