I wonder how many pilots have experienced enough biennial flight reviews to know absolutely that they are a load of crap.
I think it very much depends on who you do them with and your own attitude towards your own flying skills and knowledge.
A check ride of any kind is worthwhile even if you think you're fully up to speed on everything - having someone else putting you on the spot to deal with situations and emergencies is beneficial, you have to revisit your regs and handbooks to ensure you know them well enough, and it's a chance to get out and just get someone to critically look at your habit patterns and procedures with a view to improving them where needed.
Particularly for someone who spends almost all their flying time without supervision, I reckon they're essential.
If you're flying with instructors who can't do what they're asking you to do, go somewhere else!