As JcKent says keeping things separate and easily identifiable is undoubtedly a biggie!!
The Big negative is the Bank Charges..
Banks have a tendency to charge business customers higher costs than personal banking customers..
(even if physically you are one and the same as a sole trader!)
But depending upon the size of your business & your own personal financial situation.. you may need to be arranging business loans / overdraft facilities etc.. in which case the bank would probably be more reluctant to start offering these business type finance arrangements to a personal customer.
There are still various wholesalers / supplier who deal with "Trade only"..
and may require evidence of a business bank account to confirm you are a trading business.
Again some suppliers offer trade credit accounts.. collect goods with purchase order number payment following invoice 30day / 60day terms,
Some trade accounts are only permitted after you can show you have been trading for a certain No. of months .... (again a business account statement can be used as evidence).
Some of your regular business expenses can be set up via direct debit...
e.g. advertising / Part p scheme fees / NI contributions / Business mobile phone account etc.. again easier kept separate from personal finance DD's.
Generally Banks are happy to offer a bit of help to new start business..
e.g. zero charges 1st year, 33% charges 2nd yr, 66% charges 3rd yr,
full charges 4th year & onwards... (or similar type thing.)
There are often some useful free booklets about controlling your business costs / VAT / Insurance etc.. etc.. (Well I was given some anyway! :| )
Once your business is up and established...
raising extra finance at a later date can be far easier if you have had a reasonably healthy business bank account running...
& the bank has a pretty fair idea o your turnover just by looking at how much has been paid in over the past 12mnths!
whereas you personal account......
may be a joint account.. with other stuff going in as well!!
Thats a few thought for starters!