My significant other is remodelling our bathroom himself, and has tiled the entire floor. My mother has said not to put heavy things such as a shower, toilet, or sink directly down on the tile as it loosens, and can later cause water damage underneath- she also has asked others at Home Depot and they agree with her. My boyfriend says this isn't true and we don't need to worry about it.

Help- what do I do- how can I prove otherwise that my boyfriend is mistaken- and there shouldn't be tile underneath a corner shower???

Thanks for any ideas or comments you can provide!