Higher trading volumes are HFT's "largest, longest lasting, and most visible impact," according to Credit Suisse.
The report said:
"We estimate that volume from money managers and investors, both active and passive, has remained fairly consistent for at least a decade (between about 3 and 4 billion shares per day). Total US volumes today, however, are more than double what they were in the pre-crisis, largely pre-HFT years. The difference is mainly due to HFT and high speed trading strategies."
There are complaints that this activity isn't "real" activity, but rather that this increase is down to unnecessary trading, or is designed to take advantage of slower moving investors.
"While that can be true ... a majority of HFT activity serves to connect those natural buyers and sellers and reduce waiting times, often substantially so," Credit Suisse said.