Better mud clearance. lower BB. slightly faster steering (assuming you are switching to a 27.5 fork with greater offset.). Stronger lighter wheels. Cheaper tyres.
pretty much win win win win win win in my book*.
If you’re planning on just using your 26″ fork. You might want to try and use a tall stack lower headset cup or run the fork 10-15mm longer. (Depending on your geometry preferences)
BB height should be a fairly noticable difference. Coves had fairly high BBs. cotics BB height is lower but not really low or anything.
Low BBs are ace once you get your head round it.
*Available in antique book shops under A for AWESOME in the free thinking section.