This matters in terms of what rules govern them, and this explains why for example exchanges that aren’t registered to trade securities can trade BTC and ETH, and why we have a BTC futures trading on the CME.
The same is likely true for other coins, so far Siacoin and EOS have both settled lawsuits with the SEC. Those settlements implied that while Siacoin and EOS aren’t securities, their initial coin offerings (ICOs) did violate securities laws.
This implies that although cryptos aren’t securities in general, crypto companies still can’t do public offerings without following SEC rules (I.e. can’t sell in the US without following rules which in overly simple terms include selling to accredited investors only and filing out some forms).
DOES CRYPTO HAVE TO BE EITHER A SECURITY OR COMMODITY?: A thing can be a commodity and a security, but from CFTC and SEC statements, it seems to be the case that at least Bitcoin and Ethereum aren’t. Further, a thing can not be a security, but have a sale that is a securities sale (for example EOS and Siacoin seemed to break securities laws with their ICOs, despite the actual coins not being labeled securities by the SEC).