The big thing tomb enables is gaining cards specifically to trash them. For instance, babying along a Moneylender as a terminal silver costs a gain and is generally bad if your +buy means you need to spend $3 or more on it (possibly even if you need to spend $2 for an extra +buy). Tomb, however, makes Moneylender into a mini-Monument. Not great for mass build out (what with needing to line up paired stop cards), but good enough to spend a gain on a +buy instead of a silver. Many other cards like Spice merchant, Upgrade, or Amulet can all encourage you to fiddle around with gain & trash. More interestingly will be the setups where you can chain gains in order to increase the number cards you get to trash - gaining Feodum so you can Sacrifice 4 times for 6VP.
One place this can be a crazy good source of points is with Wt. Any surplus +buys can become a point each until the copper/curses run out (and they might). Getting to 5 VP a turn and still being able to buy a province is quite doable. With enough +buy possible on the board, you want to think hard about gumming up a Wt deck instead of churning copper to the trash for VP.
Another nice shot is with Salt. As cost efficient as Islands and can end the game quickly. Salt/Baths is somewhat viable on its own, but when you take a Salt Bath in a Tomb you can even more quickly hammer through the Province pile while getting decent points for a rush.