One reason to tile under the vanity is because you might want to replace it at some point. I know that over twenty years or so, my mother had the same tile in the bathroom but changed the vanity at least once (including going from a wall-mounted sink to a vanity at one point).
As for tile and the vanity, you can do it either way. On a custom home, the cabinets are usually put in before the floor. It’s a cleaner look. But if you’re buying your vanity from HD, then it probably is meant to be put on top of tile. You usually want a 4" high toe kick, so you lose an inch if you tile after. Check your vanity to see.
The only real issue with tiling before, is that you are putting wood (vanity) across grout lines, so it won’t be as clean looking as when you tile up to the toe kick.
Thanks for the tip, I’ll be sure to ask about this.
This is a good point. If I’m tiling under the vanity, then to get a cleaner look, I should probably choose a vanity that has four legs, something like this
St. Paul Classic 30 in. Vanity in Antique White with Stone Effects Top in Avalon
Model # CL3018P2COM-AW
A lot of people seem to like the “furniture” look of that type of vanity. Keep in mind that it’s probably going to wobble a little unless your floor is perfectly flat, so you might have to fiddle with the bottom a bit to make sure it sits squarely on the floor.
Any cabinet should be shimmed level then fastened securely to the wall with three inch screws into studs. It should not be wobbling or moving in any way. Cabinets with legs should have adjustable feet.
There is really nothing wrong with not tiling under the vanity if there is toe kick. Unless you are installing a temporary vanity it is unlikely to be replaced in a future renovation without the floor being done also. I think
Whether to use extra thick wax seals, a flange riser or to unbolt and raise the flange when reflooring is often dependent on the particular situation. Doubling up wax rings is not as reliable but the extra thick ones work fine.