Slowing down markets is not a very recent idea; for archeological interest, I recommend:
The basic argument is the following: if you allow to trade at a frequency that is faster than the natural frequency of information issued on the tradable instrument, you may face an increase of useless volatility.
Remember that in essence, we should perceive volatility as
- being good when it reflects the incorporation of information in prices (the price moves for a "good reason")
- being bad when it stems from illiquidity oscillations.
For fans of Market Impact: the first effect corresponds to permanent market impact and the second to temporary market impact.
This is an abstract view; in practice how do you know the speed at which information form prices?
- you have pure idiosyncratic effect: f.i. a company issues a new patent.
- you have sectorial effect: f.i. people are no more going to movie theatres and watch movies on platforms.
- you have correlation effects: f.i. company A and company B have the same suppliers, even if they are not in the same sector or industry.
- you have geopolitical effects: f.i. because of terrorist bombings shipping companies have to use another route.
Thus it seems difficult to know why is the proper frequency (even if the idea is seducing). They are a few elements that we can conclude by basic reasoning, like the fact that FX should trade more frequently than most companies, since almost any existing information has an influence on the relative strength of two currencies.
To conclude, let me reformulate my answer in terms of liquidity risk: what is the risk you face of holding a specific asset during 5 minutes and not being able to trade it? This is a (il)liquidity risk. Fundamental analysts' recommendations will be followed only if this risk is perceived as "small enough". And if we wait to get information to open trading, all market participants will be in the same direction, hence the asset will be very illiquid and mis-priced... Continuous trading appears to be a good option, or at least the best of all options we have in a realistic world.