As far as rock bottom, whoever told you that Rock Bottom is for technical diving only vs. recreational diving is an idiot. It's far more important for recreational diving. That said, how do you know when to start your ascent if you aren't calculating Rock Bottom? You can choose whether or not to pad the SAC rates up to 1cfm, and whether or not to factor it in for 2 divers, but padding SAC rates and calculating for 2 divers is far more important on rec dives than tec dives. Think about it. Recreational divers are generally less experienced, generally have higher SAC rates, generally take longer to get things corrected before being able to make a safe ascent, are more likely to need to borrow your gas due to not paying attention to their SPG, and may be more prone to having equipment failures due to rental gear *this is debatable, but I've seen more hose leaks and o-rings burst on rental gear than personal gear*. All that factored in means planning for a 2cfm gas requirement for ascent is much higher on my priority list in a recreational dive than it is on a technical dive. 80ft dive on an AL80 means start your ascent with 1400psi, 1100 on your 120. That gets you to the surface with 200psi which is a reasonable buffer.