A. Every home is different. Heavy wear dictates sealing more often. A home with two dogs, three kids and lots of activity may require sealing floors ever 2 or 3 years. A foyer in a two adult household, and an entrance used only for guests may go years without needed to reseal.
In a stone shower sealing needs are also affected by your water’s mineral content. Hard water would necessitate frequent re-sealing. Same with the cleaners you use. Use a pH balanced nonacidic cleaner like Aquamix Concentrated Cleaner. The wrong product can strip the sealer from the stone.