Under (default) investor rules, you recognize income (or losses) only on sales or dividends (or taxable reorganizations), and can get long term capital gains, have a low limit on offsetting losses against ordinary income, can carry forward excess losses forever, and have the wash sale rule.
Under trader rules, you must recognize gains (or losses) at the end of each year, and don't get capital gains rates, but you can offset income with losses all the way to $0, loss carryforward is time limited, but you can also carry back a few years.
I'll keep my tax deferral and long term capital gains rates, thanks; but if I were a frequent trader, it seems like the alternate regime is simpler.