SCCS (Source Code Control System) is no longer being enhanced or improved. The general consensus has been that this tool is clumsy and not suited to large numbers of users working on one project. Actually, SCCS interleaves all the versions; but it can make new development get progressively slower. Hence, SCCS is NOT recomended for new projects, it is still there to support old code base in SCCS.
RCS (Revision Control System) is often considered to be better than SCCS. One reason for this is that RCS baselines the most recent version and keeps deltas for earlier ones, making new development faster. Additional discussions concerning SCCS vs RCS is at http://www.faqs.org/faqs/unix-faq/faq/part7
Note that RCS learned from the mistakes of SCCS...
CVS, which requires RCS, extends RCS to control concurrent editing of sources by several users working on releases built from a hierarchical set of directories. "RCS is [analogous to using] assembly language, while CVS is [like using] Pascal".