Variability-intensive systems (VIS) form a large and heterogeneous class of systems whose behaviour can be modified by enabling or disabling predefined features. Variability mechanisms allows the adaptation of software to the needs of their users and the environment. However, VIS verification and validation (V&V) is challenging: the combinatorial explosion of the number of possible behaviours and undesired feature interactions are amongst such challenges. To tackle them, Featured Transitions Systems (FTS) were proposed a decade ago to model and verify the behaviours of VIS. In an FTS, each transition is annotated with a combination of features determining which variants can execute it. An FTS can model all possible behaviours of a given VIS. This compact model enabled us to create efficient V&V algorithms taking advantage of the behaviours shared amongst features resulting in a reduction of the V&V effort by several orders of magnitude. In this paper, we will cover the formalism, its applications and sketch promising research directions.