I guess it depends on your circs/what you are hoping to achieve....
In the house we sold and moved out of just before Christmas we put in a downstairs shower room, but when we bought the house there had already been an annex (with kitchenette and bathroom) added to the downstairs layout and whilst this configuration didn't suit our requirements (nor did the avocado suite, lol!), we felt that as we were intending to sell (made a mistake with house location, not intentional flipping) we would increase our target market if we retained a downstairs bath/shower room of some sort.
We actually completely reconfigured the space, opening it up into a large living room with attached shower room (in a different location to original bathroom) and felt it could be utilised as reception space, bedroom or teenage/granny annex as required by future owners.
It was certainly appreciated by those that viewed - and the family that bought - our house. We believe it helped us achieve a sale within five weeks in an area where properties tradional,y take up to a year to sell......
I should add that in addition to this shower room we had a further bathroom and shower room (ensuite) on the upper floors.