QNIM
I don't think anyone here is suggesting it shouldn't be taught, it's just not something that should need to be used on a daily basis as a means of losing height because you screwed the approach. Flapless approaches, forced landings etc are all taught but generally not used in day to day operations. I would say sideslipping falls into this category.
I would definitely discourage it's use for day to day approaches. It's uncomfortable, gives erroneous readings on pressure instruments, can cause engine probs as already discussed and is unnecessary. Maybe more emphasis should be placed on making students focus on their airspeed and profile rather than practicing a bail out option.
If you're flying privately however and get a kick out of sideslipping then why not? Keeping in mind that every crosswind landing is a sideslip, which I'm pretty sure is what the syllabus is getting at when it says "side slip aeroplane"
