Related to this, i understand kraken values its trading engine resources highly. I really think you should krank down the decimals allowed for prices. 5 decimals at 600 eur per btc is insignificantly low compared to transaction cost and spread, especially with these kinds of volumes. I sometimes see bots trying to outbid eachother for 0.00001 price differences, which does almost nothing for the spread nor trading volume but takes up just as much resources nonetheless. Incidentally it also makes it much easier to see what average price at size is going to be when looking at the orderbook.
I'd say 2 decimals is more then enough, which is relatively still higher then the ticksize in fiat forex, where volume is much higher, volatility lower and transaction cost much smaller. Also bitstamp does it succesfully being one of the biggest players.
Anyone wants to weigh in on this?
Yes, you are correct, the additional granularity really doesn't help the marketplace. It's not disastrous, but it creates an incentive for certain types of bot activity that doesn't really benefit the liquidity of the exchange. I say this as a bot operator who profits a little bit from this sort of activity. At today's prices, I would go further and say that 1 decimal is plenty (making the minimum spread about 1 basis point).