An example would be having Simmonds and Gabriel on the 4th line one night and then having Spezza and Ho-Sang another night.
We don't know if we are playing a skilled team like Tampa in the playoffs or a bruising team like Boston use to be. Also applies to the regular season as teams are configured differently.
Being able to have a roster that can do both is another card for Keefe to play that isn't available to him because of shitty cap/roster planning.
The thing is, Boston and Tampa did not have guys like Simmonds or Gabriel in their lineups. Neither had pure enforcers who can only play 5 minutes like Gabriel, and Tampa actually dumped some guys with grit because they did not have enough skill. Eventually they added some skilled grit back with Coleman, Bogosian, and Goodrow, but that was at the TDL. Boston's depth guys over the years (Nosek, Acciari, Kuhlman, Kuraly, Wagner, Haula, etc.) actually play a game that is more reminiscent of Semyonov and Brooks than Simmonds; two-way skill with a special focus on the defensive end, hounding the puck, and great skating ability. Simmonds, at best, has/does one of those three things. You will also notice that while stocky, none of those guys are particularly big nor do they commonly get into fights.
Patrick Maroon is the closest thing to Simmonds that either team has in their lineup, and Maroon has played significantly better than Simmonds the past few years. If Simmonds can return to his pre-injury play, then maybe he can be a Maroon for us... But he has to work his way up to that and prove it, because he had maybe a dozen game stretch where he was anywhere close to that useful/good.
Also, come playoffs, there is no cap. So if we want to rotate in a guy like Simmonds, cap won't be the reason it does not happen. Even during the regular season, there are ways we can make it work. If our "shitty cap/roster planning" is resulting in a 13th forward having to be waived and kept on reserve rather than permanently occupying a 13th forward spot on our roster, then there will be a lot of envious teams out there.