The spread on SBD and Steem on exchanges, especially the internal exchange, is typically very high. I've seen it as high as 17% !! If you want to do it quickly, having to change to Steem adds a huge cost to the process. Using the 'convert to steem' option takes a week.
Edit: For example now on the internal exchange the spread is 1.35%. The order books at those prices are also incredibly thin, so slippage is involved for even small amounts.
RE: You can use Steem to pay for pretty much anything worldwide - but nobody does!