Anyway:
>>>Are there any negative sides to voluntary VAT registration?
Yes, admin burden is significant. Potential to have a VAT inspector trawl thru your records could be unpleasant.
>>>>I have a small business and on many purchases you get VAT back if you're registered. If I did, would I still get VAT back on purchases even though I haven't reached the threshold for compulsory registration?
Yes.
>>>>> And except for the added paperwork, are there any negative sides to it at all?
Of course - a higher cost to your customers for one! If your customer base is to businesses (who are likely to be VAT-registered themselves) then this may well not be a consideration (altho your customers may prefer you to be VAT registered rather than not). However, if you have a largely consumer base, the imposition of VAT on your selling price may make you uncompetitive in the market place if your competition isn't VAT registered.