Unless they're going to warm the tea-pot, let it brew for 3-4 minutes, pour the milk in first then it won't make much difference.... But it's a start.
I strongly dislike tea, but my understanding from some saddos who do drink it, is that some enzymes in the milk react with the tea leaves to create a natural sugar if you put the milk in first, resulting in an altogether nicer drinking experience. Still tastes bloody awful though.
If you're making just a quick cuppa for yourself (ie just a mug and a tea bag) then by putting the milk in first you eradicate the discolouration of the mug that is caused by leaving the teabag in on its own. By doing it this way, a mug can be re-used 3 or 4 times before it needs to be washed.
By putting the milk in first you lower the temperature of the water to below optimum brewing temperature. Always wash your mug and never use water that has been previously brought to a boil. Also, the water should always be in motion throughout the brewing process.
Ringtons is better. Tea leaves and a pot trumps all. Except for the gingery, cinnamony coffee/hot chocolate thing I made last night. That was wonderous.
And flaming health freaks. I use my mug over and over. I also don't put milk in til its brewed for 3-4 minutes minimum. If you take sugar put that in before the water then it will mix evenly throughout the mug rather than gradually getting sweeter as you reach the bottom. Too many folk these days are incapable of making a proper cup of tea and it saddens me just how many people take the tea bag out as soon as the waters in the mug, add the milk and then the sugar last. It's like a hot cup of watered down milk. And vile.
Milk in last. Tea bag needs to stew a bit first. Cup don't need washing, a quick rinse is fine. Mate of mine used to leave the bag in. I tried that once. Once.
Dunno if I was clear, but, he used to make a cuppa, then drink it all with the bag still in. Was awful by the bottom. If that was clear, what the chuff are you on about??