Question: Q: "Do You Need to Use Backerboard Before Installing Tub/Shower Wall Tile...

...or can you you install the tile directly to the drywall or greenboard?"

Answer: I've seen tiling guides that blithely recommend installing the surround tile directly to drywall.

Is this possible?

Installing Surround Tile Directly on Drywall

Under limited conditions, I grudgingly admit that you could do this. Two conditions must be met:

1. It's a shower-tub combination, not shower. In a shower, you would have tile far down--meeting up with the shower pan--and this tile would receive a lot of water contact.

1. The shower-tub doesn't get much usage. Maybe it's located in a guest bathroom, and it only gets used 7-10 days a year.

But Why Risk It?

Tile, with its seams and numerous avenues for moisture infiltration, can eventually lead to the drywall being soaked. Once the drywall is soaked, the studs begin to dampen. Mold, mildew, and rot result.
In short, tile and grout are not inherently waterproof.

Opt for a more effective method of backing your shower/tub tile.