The step sequencer's great if you want to prgram e.g. Session Drummer, or a similar sample-player.
It has some serious bugs/irritations if you want to use it to control a synth though. For example, if you insert MIDI CCs other than the few "pre-set" in the pull-down controller list into a pattern, then drag out a copy, cut the clips apart and unlink the second clip, all those MIDI CCs will be lost in the newly unlinked clip (Cakewalk have acknowledged this bug).
The assumption that some CC numbers are only used for one thing is a pest as well - if you use the CC the SS pre-assigns to "pan" for example, then the pane where you insert the values only allows you to enter an offset from a central "zero" point, rather than the usual 0-127. Some way to see what the CC values actually are, rather than trying to guess them from the height of the bars would be nice as well.
Having said all that, I use the SS quite a lot - it can do useful things the PRV can't (e.g. set probabilities that a note will/won't be played).