The optimum grab rail design is different for everyone, but generally the design for “someone with limited agility” is different than for someone using a wheel chair.
For people with limited agility, it’s often best to have close walls, and close grab rails.
For people in wheelchairs, often the most important thing is to be able to wheel up close to the pan. This is called accessibility, the ability to access the facility :), and accessible toilets are specified with this primary requirement. This puts limitations on the grab rail design, and no, the grab rails aren’t optimally helpful to most people. But it seems agreed that having them is better than not, and that being able to get the wheelchair in and around is more important.
I don’t use a wheelchair. I have to read standards a lot. Before there were standards, people used to get a lot of grief with the conflicting ideas for building for people of limited agility, and building for people in wheelchairs. Now that there are standards, nobody expects to be pleased, and nobody expects to be unpleasantly surprised.
One of the critical skills/abilities a wheelchair bound person needs is the ability to manage a transfer from the wheelchair to another object - be it a bed, normal chair, commode, or toilet. Even with little to no strength in the legs many can do so with carefully choreographed movements. Some need assistance, but it you have two working arms much can be done. A lot is about getting balance and pivot points worked out, so you place the feet in the right position and pivot over them, with maybe the need to reposition the feet once, and the repositioning done when the rest of the body is in a stable position. Having the right set of handrails and bars can make it quite possible for many wheelchair bound people to manage toilets fine. Even aged or weak ones.
As noted above, being able to get the wheelchair in the right position relative to a toilet is also key. Doing a 180 degree turn isn’t easy as you need to swap the feet, but a smaller pivot where the feet need not move is vastly easier.
There are similar issues with showers, although slippery wet floors tends to make things a lots dicieer.
accessibility, the ability to access the facility :), and accessible toilets are specified with this primary requirement. This puts limitations on the grab rail design, and no, the grab rails aren’t optimally helpful to most people. But it seems agreed that having them is better than not, and that being able to get the wheelchair in and around is more important.