The rails and seats are only as strong as the wall they are installed onto.
If wall studs are not in correct locations noggins may need to be added, if access can be gained from the other side of the wall this can save pulling tiles off. If the wall is masonry/brick the installation is simple with screws and wall plugs.
For public buildings we recommend the wall is reinforced with noggins or installed into wall studs for each bracket.
For private bathrooms the weight and strength of the user needs to be considered, usually we recommend installation into the wall studs at each bracket however some installers will install into just tiles depending on the customer and bathroom.