I have mixed emotions about it.  Where I used to live it was a total scam.  You paid for an emissions check (paid to the county) and if it failed you had to go to one of their approved mechanics (who paid the county) with their printout of why you failed.  The mechanic tried to fix it and gave jou a print out of what they did to fix it which you had to turn in when you paid to get a second e-check.  If that failed you had to repeat the whole process.  If you failed on your third e-check (paying for the e-check threr times and an approved mechanic twice) they let your vehicle through anyway, they just noted it.  They didn't actually keep any vehicles off the road, they just made sure you spent a bunch of money.

There are also workarounds to fake emissions.  Many cars have an air injection system which forces air into the exhaust system making the ppm of hydrocarbons at the tailpipe test lower but they don't actually reduce the total amount released.  Cheats like that pass an emissions check and makes everyone feel better but don't actually do anything to reduce pollution.