Underlayment and membranes
The real weather protection on any roof is the layer you cannot see. Synthetic underlayment sheds water that gets past the surface and does not rot like the old felt. Self-adhering ice-and-water membrane seals around nails and is used in valleys, at eaves and around penetrations. On a re-roof, upgrading these two is the best money spent.
Tile roofs in particular depend entirely on the underlayment; the tiles are mostly there to protect it from sun.
Sealants
Roof sealant is for small joints: the top edge of flashing, the collar of a pipe boot, an exposed nail head. It is not a repair for a flashing that was installed wrong, and a roof with sealant smeared everywhere is a roof someone has been chasing leaks on. Use a polyurethane or silicone product rated for roofing; the cheap tubes crack in one summer here.
Clear shingle sealants that bond a lifted tab back down have a place after wind, but the tab is usually better replaced.
Coatings
Elastomeric and silicone coatings go over low-slope roofs and some metal roofs to seal minor cracks, reflect heat and extend life. A white reflective coating on a commercial flat roof is the standard cool-roof approach here and makes a real difference to the building below in summer. They do not belong on shingle or tile.
A coating over a failing membrane is a delay, not a fix; the membrane still needs to be sound.
Wind protection
High-wind rated shingles with a wider sealant strip, extra nailing per the manufacturer's high-wind pattern, mechanical ridge systems on tile, and properly clipped hip and ridge caps. These are installation choices, not products you buy later, which is why the re-roof spec matters.
In Santa Ana country I always spec the high-wind nailing pattern.
What to skip
Miracle roof rejuvenator sprays that claim to restore old shingles, driveway-grade sealers used on roofs, and any coating applied over dirt and loose granules. They cost money, do little, and can void what warranty the roof still has.
If a product sounds like it replaces a re-roof for a fraction of the cost, it does not.
Where to spend
Put the money in the underlayment, the flashings and the installation details; those are the layers that keep weather out for decades. Treat sealants and coatings as maintenance on top of a sound system, and be suspicious of any product sold as a substitute for doing the roof properly.