Hi Simon,
The primary function of the bypass is to simulate an additional load, but it can help in other areas too. If you don’t have a neutral at the switch (which most people don’t), some lights can dim a little unevenly without a bypass. It’s generally only cheap ones, it’s pretty negligable and really depends how particular you are about lighting design - most probably wouldn’t notice it, but I’m quite picky. The bypass smooths the dimming curve out a little bit and ensures you get nice, even transitions. The way in which we perceive light is logarithmic, but a lot of cheap LED driver circuits are set up for linear, so the top end of the brightness curve can appear to dim slower than the bottom end. Does that make sense? Kind of hard to explain without going off on a massive diatribe!
You’re absolutely right, though - by putting a bypass in, you future-proof yourself against future lighting upgrades. If you’ve got incandescents now and you upgrade to LEDs in the future, it saves you having to fish around in the backbox / ceiling cavity and add the bypass. If you plan to leave the system in situ when you move house, the bypass ensures it’s going to work with whatever lighting loads the new owners throw at it. If future generations of LED are even more efficient and every lighting circuit in the house ends up below 60W… you get the picture.
Is it cost-effective to install them day one? No, not unless you’re paying an installer for their time. Is it good practice? Definitely, if you can stomach the extra £7ish per circuit.
We’re told the new Bypass will include “extra intelligence” that allows it to work more effectively with the Dimmer than the old one… but I don’t have any verified information on that. Apparently it’s out in two to three weeks, but there’s no official launch date yet so assume longer.
Any more questions, let me know!