Long time, no chat!

I'm currently in the market for a folding bike, and have made a few selections online (FLBS has, I think, a few folders but they're out of my price league - IIRC it's only Fuji bikes in there). I've browsed through a few articles in this subforum and I'm reconsidering my original choice, a relatively inexpensive (~250USD) folder with 26", and I am considering a 20". I am a very small individual - only 5'3" if you include the "lifted" heels I was born with - so it's unlikely any size will be a problem. My main motivations are something easier to lug onto the bus - some have front-racks, others let you wheel them on but man is that all awkward - and I'm going to be moving into a new place and would like something easier to carry up stairs.

Anyways now that I'm looking through and figuring out what I want, I've realized I haven't spotted a thread that highlights the DOWNSIDES to a folding bike. Or, more generally, why would one be compelled to choose a non-folder over a folder for "regular" (non competitive) cycling? My current non-folder is a general purpose bike - I commute with it, I shop with it, I go places with it. What advantages would my current 21 gear 26" wheel bike have over a "folder", to use that word in a vaccume?

Thanks,

M.