some languages spell it relais - not sure the point of correcting some one.
I've seen another reason to PWM a relay coil - reduce the audible click. With a little experimentation, you can determine the pull in duty cycle and the click is reduced. the guy who did it actually create a pwm profile where pwm'd it fairly high for 10s of mS and then backed off while the contact "coasted" into place. He did an inverse profile for turn off. it was quite a bit quieter. this was for a piece of equipment that went into a library and they had completed the HW when the complaint about the clicking came up. A better solution would be an SSR but this solved the problem with out a redesign. pretty clever. I wouldn't do this for higher current relays since the slower pull in would increase the arc time.