Juncture of tub and separate shower

Am I asking for trouble if I butt a shower right up to a tub?

There are occasions when I can raise the tub and thus bring the shower waterproofing and tile vertically up 4-6", but when I can't do that, am I going to run into problems at that juncture? Maybe yes with a steel tub, but definately yes with a fiberglass tub? Or with the materials changes with temperatures and/or weight, will there be movement no matter what?

Any way around this?

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Are you talking about a framed-up wall between??

No wall between. Ideally for some design/client needs, the tub is right "on" the shower floor so to speak. And maybe that's the answer - to tile the whole space, for instance ≈5' x 7' and simply put the tub along the 5' wall, leaving a shower that's about ≈5' x 4.5'. (These showers are tiled curbless showers)

However - a) given the cost of materials and labor, tiling may not be necessary
and thus, would it make sense to just waterproof it?
b) even if waterproofed, if water starts seeping in under the long edge of the tub that's against the shower, wouldn't it start getting a little "funky" under there?

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