i bought a bike its got an exposed bottom braket. whats the advantages/disadvantages?

the word exposed has too many different meanings for that to make any sense. if it's not a cutout at the bottom of the shell, please attach a picture or explain further.

EDIT: yeh, actually the cutout is the most reasonable assumption

I assumne there is a slot cutout in the BB shell on the frame

Advantages:
looks cool(especially if you have a fance-pants BB, like a campy one where the logo would show through)
Drains water that gets into the frame

Disadvantages:
water/mud/crud could splash up in there and muck things up.

Assuming your use a sealed cartridge bottom bracket like this:

you should be fine as the bearings are more or less sealed from the elements.

If you use an adjustable BB with an exposed cup and spindle system like this:

, expect to rebuild your BB often if you ride on the street. At least once a week, more if it's wet outside.

?!?!

Are you for serious?

Perhaps one of the newer mtb bbs that place the bearings outside the bb shell so bigger bearings can be used.
https://photo.pinkbike.com/photo/433/pbpic433815.jpg

I rebuild my bottom bracket daily. What?

+1

A properly assembled adjustable bb can take months of abuse without needing to be serviced. Even when it's wet, unless "wet" means highly pressurized water.

Me too. But only after stripping and repainting the frame.
And I install a new headset every other day. Daily seemed like overkill after a while.

I agree, but when you have GIANT HOLES IN YOUR BB SHELL, there is almost nothing keeping road grit from entering your bearings if you used a cup and cone style BB.

or https://harriscyclery.net/itemdetails.cfm?ID=1073

is it a bottom bracket similar to this?

if so...this set up lets you run a splined crankset (has a stiffer interface between spindle and crankarm) on a sturdier bb than before. in days past, bottom brackets had a square tapered spindle (as pictured above) and the spindle fit nicely in two sealed bearings in your bb cartridge, which then threaded nicely into your frame. then companies decided that some modernization was necessary so they designed a splined bb spindle for a stiffer crank/spindle interface. only problem was that the outer diameter of the bearings remained the same to fit in the cartridge (and frame) while the inner diameter was also increased to make room for a larger diameter spindle. this made the bearings thinner, which made them more likely to crap out on you over the course of a few months. the next "innovation" was to move the bearings out of the bb shell, which enabled manufacturers to use a larger sealed bearing without regard for the confines of the bb shell. one minus is that these bearings sit outside of your frame, exposing them to the elements, so while they may not wear as quickly, they can get gummed up in particularly nasty conditions. phil wood has come to the rescue effort by bringing cyclists everywhere their infamous bearings that can be retrofitted into your existing bearing cups...giving you a silky smooth crankspinning feel for years to come...well, not really...but for a good long while.

of course, if your bottom bracket doesn't look like this, feel free to disregard everything i've said

^ thanks for the description, i've seen several like these before, and was not entirely sure as to the reasoning behind them.

Ha, beat me to it!
I should note that no LBS around here carries these bb sleeves, but as rollsroyce points out, they're available online.

But, um, has the OP given up on this thread?